feat: GPU-native CAGRA filtered search via bitset

Override VectorIndex::search_with_filter for CagraIndex: builds a
bitset from the predicate on host, uploads to GPU, and passes it to
CAGRA's traversal-time filter via search_with_filter (patched cuvs).

Eliminates the 3x over-fetch workaround — k=100 goes directly to GPU
as k=100 with a bitset, not k=300 unfiltered + post-filter. Better
recall for type-filtered and language-filtered queries.

Also:
- Cargo.toml [patch.crates-io] pointing to ../cuvs-patched (local
  patched cuvs 26.4 with search_with_filter, upstream PR
  rapidsai/cuvs#2019)
- Demoted CAGRA itopk_size clamp warning to debug level

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jamie8johnson