PERF: Improve merge performance
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

this avoids a bunch of unnecessary checks, might be worth it


```
| Change   | Before [b2b1aae3] <merge~1>   | After [aebecfe9] <merge>   |   Ratio | Benchmark (Parameter)                                                                       |
|----------|-------------------------------|----------------------------|---------|---------------------------------------------------------------------------------------------|
| -        | 46.9±3μs                      | 41.9±0.5μs                 |    0.89 | join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 'monotonic', 0, True)     |
| -        | 210±7ms                       | 187±5ms                    |    0.89 | join_merge.I8Merge.time_i8merge('left')                                                     |
| -        | 2.11±0.2ms                    | 1.88±0.01ms                |    0.89 | join_merge.MergeEA.time_merge('Float32', False)                                             |
| -        | 17.1±3ms                      | 15.2±0.2ms                 |    0.89 | join_merge.MergeMultiIndex.time_merge_sorted_multiindex(('int64', 'int64'), 'inner')        |
| -        | 1.06±0.04ms                   | 907±20μs                   |    0.86 | join_merge.Merge.time_merge_dataframe_integer_2key(False)                                   |
| -        | 7.99±0.9ms                    | 6.82±0.06ms                |    0.85 | join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 'non_monotonic', 1, True) |
| -        | 224±10ms                      | 191±6ms                    |    0.85 | join_merge.I8Merge.time_i8merge('inner')                                                    |
| -        | 513±90μs                      | 425±5μs                    |    0.83 | join_merge.ConcatIndexDtype.time_concat_series('string[python]', 'monotonic', 0, False)     |
| -        | 519±100μs                     | 421±2μs                    |    0.81 | join_merge.ConcatIndexDtype.time_concat_series('string[python]', 'non_monotonic', 0, False) |
| -        | 1.18±0.6ms                    | 751±7μs                    |    0.63 | join_merge.ConcatIndexDtype.time_concat_series('int64[pyarrow]', 'has_na', 1, False)        |

```
@WillAyd good to merge? This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. I think we would want this, but it appears this has gone stale so going to close to clear the queue