Improve test coverage

[MovAh13h]

This PR adds comprehensive test coverage across the library, filling gaps left by earlier implementation work.

• Added tests/bloomable.rs covering all Bloomable primitive implementations (integers, floats including NaN/infinity, bool, str, String, byte slices) and a with_params consistency check
• Extended tests/serde.rs with a manual cuckoo_filter module covering empty, populated, and with_buckets round-trips (the macro couldn't handle CuckooFilter's single-arg constructor)
• Fixed round_trips helper to accept ?Sized types so str and [u8] slices work correctly

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