Implement maybe_cache for compat between immutable/mutable classes

[jbrockmendel]

Also fixes lookups/docstrings for class-level access to cache_readonly attributes.

• closes Series.hasnans shouldn't be cached #19700
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Related: wesm/pandas2#27

[jreback]

this seems like quite a lot of extra code when you could simply override hasnans for Series

[jbrockmendel]

this seems like quite a lot of extra code when you could simply override hasnans for Series

If it were just hasnans I would agree. The motivation comes from WIP to move arith/comparison ops from DatetimeIndexOpsMixin/DTI/TDI/PI to array classes, where there are currently a bunch of cache_readonlys that need to be flipped. This seemed like a reasonable scope to break off of what would otherwise be a giant diff (similar train of thought for #19672).

[jbrockmendel]

Since this is failing tests anyway, I'll remove the new pieces and just fix hasnans and the docstrings.

[jbrockmendel]

No idea what’s up with this test. Closing to narrow the queue