fix: satisfy Rust 1.98 chunks lint

[shyjsarah]

Summary

Restore the workspace Clippy check after Rust 1.98 enabled chunks_exact_to_as_chunks by default. This failure is already present on main and also blocks unrelated PRs such as #747 and #749.

Changes

• Replace constant-size chunks_exact calls with as_chunks in Murmur hashing.
• Update fixed-width vector score test iteration.
• Update Hybrid Search named-struct and options pair iteration.
• Preserve the existing even-length/alignment validation and runtime behavior.

Testing

• cargo +1.98.0 clippy --locked --all-targets --workspace --features fulltext,vortex -- -D warnings
• cargo +1.98.0 test -p paimon spec::murmur_hash --lib
• cargo +1.98.0 test -p paimon test_raw_vector_score_matrix_matches_scalar_metrics --lib
• cargo +1.98.0 test -p paimon-datafusion --test read_tables hybrid_search_tests
• Verified as_chunks compiles with the workspace MSRV, Rust 1.91.0.
• cargo fmt --all -- --check
• git diff --check

Notes

No public API or behavior changes.

[QuakeWang]

+1