Fixes #159792.

The accelerated warnings implementation used the supplied per-module registry for the "once" action. As a result, the same warning was emitted again from another module, contrary to the documented behavior and the pure-Python implementation.

Always use the global once registry for this action. Add a shared regression that emits the same warning on different lines in two modules; it fails with the unmodified C implementation and passes with this fix and with the Python implementation.

Validation on Linux x86-64 debug builds:

• test_warnings and test_logging passed in GIL and free-threaded builds (494 test cases in each; expected skips).
• ./python -X context_aware_warnings=1 -m test test_warnings passed.
• ./python -m test -R 3:3 -m test_once_across_modules test_warnings passed with no reference leaks.
• Ruff, NEWS reStructuredText lint, patchcheck, and git diff --check passed.

• Issue: warnings.simplefilter("once") emits the same warning once per module #159792