feat: CuckooFilter

[MovAh13h]

Adds CuckooFilter — a deletion-capable filter that uses ~1 byte per item vs 8× for CountingBloomFilter.

• 8-bit fingerprints, 4 slots per bucket, cuckoo eviction with 500 max kicks
• insert returns Result — fails gracefully with BloomError::CapacityExceeded at ~95% load
• remove returns bool — same correctness contract as CountingBloomFilter
• Added BloomError::CapacityExceeded variant
• Tests: construction, no false negatives, deletion, capacity exceeded, behavioural, statistical FPR
• Updated README filters table