🧪 [Testing Improvement] Exhaustive snap direction tests

[perim]

🎯 What: Added exhaustive testing for the snap function in direction.h.
📊 Coverage: The test now checks all possible 16-bit values (0 to UINT16_MAX) to ensure they correctly snap to the nearest cardinal point (0, 16384, 32768, 49152). This implicitly covers positive and negative values (due to wrap-around behavior), values close to cardinal points, and values exactly at cardinal points.
✨ Result: Increased test coverage and confidence in the determinism and correctness of the snap function. All 65536 possible states are verified locally.

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PR created automatically by Jules for task 15781837379914690619 started by @perim

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[perim]

@jules please resolve the merge conflict.

[google-labs-jules]

@jules please resolve the merge conflict.

I have successfully resolved the merge conflict in test_direction.cpp. I rebased on top of origin/main to pull in the recent upstream changes and resolved the conflict to keep both sets of tests (isinr/icosr tests and the newly added snap tests). The tests are passing successfully.