ENH: extension ops
builds on #21185 for extension array ops
pre-cursor to #21160 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21191?src=pr&el=h1) Report
> Merging [#21191](https://codecov.io/gh/pandas-dev/pandas/pull/21191?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5348e06c4e9e8a03cbd0011483d2dd087e850940?src=pr&el=desc) will **decrease** coverage by `0.07%`.
> The diff coverage is `60.97%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21191/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21191?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21191      +/-   ##
==========================================
- Coverage   91.84%   91.77%   -0.08%     
==========================================
  Files         153      153              
  Lines       49543    49618      +75     
==========================================
+ Hits        45504    45538      +34     
- Misses       4039     4080      +41
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.17% <60.97%> (-0.07%)` | :arrow_down: |
| #single | `41.86% <47.96%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21191?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `98.24% <ø> (ø)` | :arrow_up: |
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `93.14% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbW1vbi5weQ==) | `95.09% <100%> (+0.44%)` | :arrow_up: |
| [pandas/core/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbWlzc2luZy5weQ==) | `91.66% <100%> (+0.02%)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.12% <100%> (ø)` | :arrow_up: |
| [pandas/core/algorithms.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWxnb3JpdGhtcy5weQ==) | `94.5% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `59.84% <21.56%> (-24.11%)` | :arrow_down: |
| [pandas/core/dtypes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Jhc2UucHk=) | `88.09% <50%> (-4.02%)` | :arrow_down: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `87.93% <50%> (-0.13%)` | :arrow_down: |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `95.52% <81.81%> (-0.07%)` | :arrow_down: |
| ... and [4 more](https://codecov.io/gh/pandas-dev/pandas/pull/21191/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21191?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/21191?src=pr&el=footer). Last update [5348e06...f62c1cf](https://codecov.io/gh/pandas-dev/pandas/pull/21191?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Looks reasonable, with some comments on organization in `core.ops`.  I haven't looked at the tests closely yet, since I think a lot of them will disappear from the diff after #21185. @jbrockmendel note I haven't actually changed this much (IOW for your comments) yet. @jreback am I right in thinking that after #21885 goes through the diff for this PR will be much smaller (and therefore easier to review)? yes going to include directly in #21160 as much smaller now