Add validation for number of datetimes in Temporal.interval

[mo-lukecarr]

WIP, aims to address the existing TODO comment for validating temporal list lengths.

[mo-lukecarr]

Note to self: add some test cases to confirm that validation fails when lists are provided with len(...) != 2.

[mo-lukecarr]

I appear to get an error in IntelliJ on the use of Len(...) which says Generics should be specified through square brackets. However, tests are still passing locally and a quick search suggests that this is a known issue with JetBrains' inspections (e.g. non-issue).

[PaulVanSchayck]

Thanks for this draft PR. You probably need to add this snippet to make Python 3.8 happy:

if sys.version_info < (3, 9):
    from typing_extensions import Annotated
else:
    from typing import Annotated

[mo-lukecarr]

Thanks for this draft PR. You probably need to add this snippet to make Python 3.8 happy:

if sys.version_info < (3, 9):
    from typing_extensions import Annotated
else:
    from typing import Annotated

My impression (maybe wrong!) is that typing_extensions can be a drop-in for all versions, so I could amend the import to just use from typing_extensions import Annotated for all versions, rather than checking sys.version_info and conditionally importing.

Or is there a specific preference to use this approach? Happy to do so if there is!