Support for Python scalars

[asmeurer]

The 2024.12 version of the standard will implement support for scalars in functions. See data-apis/array-api#807.

This has not yet been written in the draft spec, so nothing is implemented here yet. This issue is just to track that work.

There has also been a start to this at #78

See also #77

[ev-br]

Here are the individual PRs which implement parts of this issue:

• binary elementwise functions: ENH: allow python scalars in binary elementwise functions #100
• where: Add support for scalar arguments to xp.where #78
• result_type: Allow python scalars in result_type: 2024.12 revision #119

[ev-br]

Looks like all is done here. All this needs testing in array-api-tests; shall track test additions over there, no need to duplicate it here.