ENH: Added isascii() string method fixing issue #59091
- [x] closes #59091
- [x] [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
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

This pull request introduces the isascii() string method to the pandas API, enabling users to efficiently check whether all characters in each string are ASCII. The implementation leverages the pyarrow.compute.string_is_ascii function for high-performance processing when working with Arrow-backed pandas objects. The method has been integrated into the pandas string accessor (str) via the _map_and_wrap utility, ensuring it aligns with pandas' existing API design.

Summary of Changes:

Added the isascii method to the string accessor using _map_and_wrap for dynamic registration and documentation integration.

Implemented the core logic in _str_isascii, which uses pyarrow.compute.string_is_ascii.
Added corresponding tests to verify correctness, performance, and edge cases.

Updated the whatsnew documentation to include the new feature in the upcoming version notes.

This enhancement addresses requests for additional string validation methods (closes #59091) and aligns pandas with commonly needed text processing capabilities.
I think this looks good in general. I don't think the CI failures are related - can you try merging in main to see if that fixes things? pre-commit.ci autofix Thanks @avecasey 