Parametrize tests for Series[timedelta64] integer arithmetic
Breaks up a few big tests, parametrizes, covers cases much more thoroughly including identifying a few new xfails.

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19166?src=pr&el=h1) Report
> Merging [#19166](https://codecov.io/gh/pandas-dev/pandas/pull/19166?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/982e11233698bc54e59be87eb257da2f33b8eb10?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19166/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/19166?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19166      +/-   ##
==========================================
+ Coverage   91.52%   91.52%   +<.01%     
==========================================
  Files         148      147       -1     
  Lines       48778    48773       -5     
==========================================
- Hits        44642    44638       -4     
+ Misses       4136     4135       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.89% <ø> (ø)` | :arrow_up: |
| #single | `41.62% <ø> (+0.01%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19166?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.2% <0%> (-0.22%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.62% <0%> (ø)` | :arrow_up: |
| [pandas/tools/hashing.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL3Rvb2xzL2hhc2hpbmcucHk=) | | |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.49% <0%> (+0.06%)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.58% <0%> (+0.15%)` | :arrow_up: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19166/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `92.06% <0%> (+0.17%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19166?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/19166?src=pr&el=footer). Last update [982e112...5560f07](https://codecov.io/gh/pandas-dev/pandas/pull/19166?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!