* Benches: use SmallRng instead of ChaCha12-based generators
All benchmarks used StdRng or rand::rng() (ThreadRng), both backed by the
ChaCha12 block cipher in rand 0.10. Benchmarks do not need crypto-strength
randomness, and several draw random values inside the timed closure, so
cipher work was included in the measurement itself.
Switch every bench target to SmallRng (Xoshiro256++), and key the HNSW
graph cache and sparse index cache by RNG algorithm so stale caches built
from the old generator are not reused against newly generated vectors.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Benches: replace free-function rand::random with local SmallRng
Addresses review: rand::random draws from the thread RNG (ChaCha12),
including inside the timed loop of the pq score benchmark.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>