Backport of #20750

Closes #20746

The time manipulation functions (e.g. busday_count) are somewhat unique in that they unsafely cast many of their inputs to datetime64 or timedelta64 arrays. This unsafe casting means that the conventionally used npt.ArrayLike alias is not comprehensive enough to capture all valid input types, most notably excluding datetime.date and datetime.datetime.

This PR thus expands the relevant argument types with support for more datetime-based objects.