Add `pow_mod` in math.py

[Natsume-Neko]

pow_mod is presented in original ACL, while not implemented here.

[not522]

Thanks! Python's built-in pow has the mod argument. https://docs.python.org/3.13/library/functions.html#pow
Would it be a good idea to introduce atcoder.math.pow_mod as a wrapper?

[Natsume-Neko]

Thank you for reply!
I think it would be a good idea since we can keep consistent with the original ACL

[Natsume-Neko]

@not522
I want to implement the wrapper. (May I do that?)
Then I wonder if we need additional assertion in the wrapper? And do we still need to add tests for that?

[not522]

assertion

The original implementation has the assertion, but Python's mod accepts negative exp and mod. I think the additional assertion is unnecessary as it may confuse Python users.

test

I plan to add ac-library's tests, so it's okay if your pull request does not have tests.