perf: streamline sketch update paths

[tisonkun]

Summary

• Make Bloom filter bit-setting operations report the previous bit state, allowing contains_and_insert to check membership and insert in one pass while reusing the existing set_bits and set_bit concepts.
• Add a benchmark for contains_and_insert when all queried values are already present.
• Express the Theta-family hash table resize and rebuild thresholds directly with exact integer relationships, removing the resize threshold constant and floating-point conversion from this shared Theta/Tuple code.

Performance

Measured locally with 10,000 present u64 values per iteration:

cargo bench --package benchmarks --bench benchmarks -- bloom::update --min-time 3 --sample-count 30

Benchmark	main median	This PR median	Change
bloom::update::contains_and_insert_present_u64	220.4 µs	161.8 µs	26.6% lower

The Theta-family threshold change is included as a code simplification rather than as a general performance claim: 32-byte Theta and Tuple update measurements remained close to the baseline, while shorter-input results varied more noticeably.

Validation

• cargo x check
• cargo x test
• cargo x lint