* Add HashSet implementation
Add a generic HashSet with full allocator support and standard set operations.
- Basic operations: add/remove/contains/clear
- Set operations:union_set/intersection/symmetric_difference/difference/is_subset
- Memory management with allocator support
- Iteration support
- Automatic resizing with load factor control
* Add "add_all" "add_all_from" "remove_all" "remove_all_from"
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Co-authored-by: Christoffer Lerno <christoffer@aegik.com>
