templatize timedelta arith ops
Some Timedelta operations are constructed using `_binary_op_method_timedeltalike`, while a bunch of others re-implement shared logic.  This PR is an attempt to get rid of the small differences in this shared logic so they can eventually use a single template.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19871?src=pr&el=h1) Report
> Merging [#19871](https://codecov.io/gh/pandas-dev/pandas/pull/19871?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ce77b79b97d7e827f50ebd0b7ca292fc2d966cc7?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19871/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19871?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #19871   +/-   ##
=======================================
  Coverage   91.64%   91.64%           
=======================================
  Files         150      150           
  Lines       48946    48946           
=======================================
  Hits        44858    44858           
  Misses       4088     4088
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.02% <ø> (ø)` | :arrow_up: |
| #single | `41.81% <ø> (ø)` | :arrow_up: |


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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19871?src=pr&el=footer). Last update [ce77b79...6225653](https://codecov.io/gh/pandas-dev/pandas/pull/19871?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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