REF: de-duplicate reso-casting code
- [ ] 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.

Could you merge in main once more (GHA was down)?

Also what order of the existing PRs should be reviewed/merged. Getting kinda lost > Also what order of the existing PRs should be reviewed/merged

This and #48956 should be at the top of the list; not dependent on other PRs while other upcoming PRs depend on them.

The only ones where the order really matters are #48910 then #48918 then #48923.  A bunch of upcoming stuff relies on these.

#48819 is preliminary to an upcoming PR doing the same public-ifying for the array methods and accessors.
 greenish Thanks @jbrockmendel 