Moved Array#& (set intersection) implementation from Ruby to C to improve
memory usage and performance. The C implementation uses hash-based
deduplication for large arrays (>16 elements) and linear search for
smaller arrays, following the same hybrid pattern as Array#| and Array#-.
Key improvements:
- Hash-based approach uses mrb_hash_delete_key() for proper deduplication
- Linear search approach checks result array to ensure uniqueness
- Maintains order preservation from the first array
- Eliminates temporary object creation in Ruby implementation
Added comprehensive test coverage for both small and large array scenarios,
including edge cases like no intersection, complete intersection, and
duplicate handling.
Co-authored-by: Atlassian Rovo Dev
Yukihiro "Matz" Matsumoto
ea5de2b8da