gh-116738: Add free-threading tests for binascii

[raven-dev-ops]

Summary

• Add free-threading regression coverage for binascii (gh-116738).
• Assert that importing binascii does not enable the GIL when running with -X gil=0.
• Add a multi-thread stress test for common binascii operations under -X gil=0.

Motivation

• Built-in extension modules should be thread-safe in free-threaded builds and correctly declare their GIL usage.

Testing

• Default build: ./python -m test -j0 test_binascii
• Free-threaded build: ./python -X gil=0 -m test -j0 test_binascii

Issue

• gh-116738

[python-cla-bot[bot]]

All commit authors signed the Contributor License Agreement.

[bedevere-app[bot]]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app[bot]]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app[bot]]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[raven-dev-ops]

This is the first time I have tried to contribute to an open-source project, just let me know what I am doing wrong, I am thankful for your time.