No issue: test_filecmp: Add tests for filecmp.cmp cache hit and overf…

[Bolotnyj]

Summary

This PR adds missing unit tests for the filecmp module to validate its caching behavior and automatic cache clearing mechanism.

Changes

• Added test_cmp_cache_hit to verify that successful cache hits return consistent results without computing file properties again.
• Added test_cmp_cache_clearing_on_overflow to ensure that filecmp._cache triggers a reset and effectively limits its size when capacity exceeds 100 entries.

Tested locally using coverage, ensuring full coverage of the internal cache conditional blocks.

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