Minimum Python version to 3.10 TODO

[maread99]

type annotations

• Use of Optional and Union can now be migrated to using the | operator in the following circumstances:
  • parameter annotations of functions decorated with @valimp.parse (get_type_hints did not support the | operator prior to py 3.10). For example, Optional[Union[str, float, int]] can now be annotated as str | float | int | None.
  • creating type aliases, for example Symbols = Union[list[str], str] can now be defined as Symbols = list[str] | str
  • Indeed, search across the library for any references to Optional and Union, including with the docs, and remove / revise.
• Should also be able to lose the from __future__ import annoations lines from the top of modules.
• Can probably by now revert the fix implemented to accommodate bug in pandas 2.1.0 concerning treatment of origin. Intention in BUG: In 2.1.0 .resample extrapolates indexes to any 'origin' defined with Timestamp pandas-dev/pandas#55064 was to revert in 2.1.1. Required changes to revert fix are noted in comments on the commit.

[maread99]

Would be closed by #353