ENH: maybe_convert_objects corner cases
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry


> does this have any user facing change?

not that im aware of.

motivating goal is to eventually kill off maybe_infer_to_datetimelike (along with the PR deprecating the string inference) and just use `lib.maybe_convert_objects(values, convert_datetime=True, convert_timedelta=True)` can you rebase.

maybe_convert_objects is getting pretty long...... > maybe_convert_objects is getting pretty long......

on the plus side its mostly flat (at least the recent additions are).  im optimistic we can get rid of some other conversion functions/special-casing and it'll be extremely worth it (xref #40489 could use your input)