REF: shift ravel in infer_dtype
Precursor to #24050 as requested from @jreback in review: https://github.com/pandas-dev/pandas/pull/24050/files#r243769223 / https://github.com/pandas-dev/pandas/pull/24050/files#r243769260

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=h1) Report
> Merging [#24560](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4cf985acce7df57678e0fa3aff057c7eddf56a48?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24560/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24560      +/-   ##
==========================================
- Coverage   92.33%   92.31%   -0.02%     
==========================================
  Files         166      166              
  Lines       52465    52556      +91     
==========================================
+ Hits        48442    48519      +77     
- Misses       4023     4037      +14
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.74% <92.59%> (-0.02%)` | :arrow_down: |
| #single | `43.05% <62.96%> (+0.05%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `98.01% <ø> (+0.09%)` | :arrow_up: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `95.58% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/tile.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS90aWxlLnB5) | `94.82% <100%> (ø)` | :arrow_up: |
| [pandas/core/sorting.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc29ydGluZy5weQ==) | `98.27% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/integer.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2ludGVnZXIucHk=) | `96.29% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.72% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL21pc3NpbmcucHk=) | `93.18% <100%> (ø)` | :arrow_up: |
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `96.66% <100%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.82% <100%> (ø)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.53% <100%> (-0.11%)` | :arrow_down: |
| ... and [30 more](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=footer). Last update [4cf985a...5fb02b8](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=h1) Report
> Merging [#24560](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/43b35fc07f6522b1b9f0e6132f261336dba6294a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `96.77%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24560/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24560   +/-   ##
=======================================
  Coverage   92.33%   92.33%           
=======================================
  Files         166      166           
  Lines       52544    52544           
=======================================
  Hits        48517    48517           
  Misses       4027     4027
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.76% <90.32%> (ø)` | :arrow_up: |
| #single | `43.05% <64.51%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3RpbWVkZWx0YXMucHk=) | `88.1% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `95.58% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/tile.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS90aWxlLnB5) | `94.82% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `98.01% <100%> (ø)` | :arrow_up: |
| [pandas/core/sorting.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc29ydGluZy5weQ==) | `98.27% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/integer.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2ludGVnZXIucHk=) | `96.29% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.72% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL21pc3NpbmcucHk=) | `93.18% <100%> (ø)` | :arrow_up: |
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `96.66% <100%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.82% <100%> (ø)` | :arrow_up: |
| ... and [7 more](https://codecov.io/gh/pandas-dev/pandas/pull/24560/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=footer). Last update [43b35fc...a040325](https://codecov.io/gh/pandas-dev/pandas/pull/24560?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback 
This is green, except two azure failures due to #24564 lgtm ping on green. thanks!