[3.12] gh-126876: Fix socket internal_select() for large timeout (GH-126968)

[miss-islington]

If the timeout is larger than INT_MAX, replace it with INT_MAX, in
the poll() code path.

Add an unit test.
(cherry picked from commit b3687ad)

Co-authored-by: Victor Stinner vstinner@python.org

• Issue: Assertion failure for socket with too large default timeout (larger than INT_MAX) #126876

[Yhg1s]

@vstinner this backport is broken because of a missing import of _testcapi, which exposes a different problem in the upstream change (where _testcapi is imported at the top level when it's available): the tests aren't skipped if _testcapi is None. Would you mind fixing that in main?

[vstinner]

@vstinner this backport is broken because of a missing import of _testcapi, which exposes a different problem in the upstream change (where _testcapi is imported at the top level when it's available): the tests aren't skipped if _testcapi is None. Would you mind fixing that in main?

Alright, I wrote #127517 to fix the test in main.

[vstinner]

I included my test_socket fix #127517 in this backport.

[vstinner]

I included my test_socket fix #127517 in this backport.

Oh, I didn't notice that test_socket is very different in 3.12, it doesn't import _testcapi at the module level. I wrote the test differently to make it specific to CPython.