gh-116738: Add free-threading tests for binascii

[raven-dev-ops]

Summary

• Add free-threading regression coverage for binascii (Audit all built-in modules for thread safety #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

• Audit all built-in modules for thread safety #116738

[python-cla-bot]

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[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.