Warnings and errors specific to the C implementation of the warnings module

New deprecation warnings about missing or inconsistent __spec__.loader and __loader__ introduced in #86298 are emitted only for the C implementation of the warnings module. Existing errors (AttributeError or ValueError) are also only raised for the C implementation of the warnings module. See tests added in #122227.

I believe that before turning the deprecation warnings into errors, we should add warnings for the Python implementation.

cc @brettcannon, @warsaw

Linked PRs

• gh-122255: Add black box tests in test_warnings #122227
• [3.13] gh-122255: Add black box tests in test_warnings (GH-122227) #122818
• [3.12] gh-122255: Add black box tests in test_warnings (GH-122227) #122819
• gh-122255: Synchronize warnings in C and Python implementations of the warnings module #122824