chore(lint): fix clippy 1.98 pedantic lints breaking every PR

[BenjaminDEMAILLE]

Why

main is red under the CI toolchain. Stable clippy 1.98 adds two pedantic lints that fire on existing code, and CI runs cargo clippy --all-targets -- -D warnings, so every PR opened today fails on files it never touched (seen on #235, a config-only change).

error: using `chunks_exact` with a constant chunk size
  --> src/align/simd_scan.rs:31:29
  --> src/align/simd_scan.rs:32:31
  --> src/bam_dedup.rs:317:49
error: manual implementation of `midpoint` which can overflow
  --> src/quant/mod.rs:323:27

Note for anyone who checked locally and saw nothing: cargo does not replay diagnostics for crates that are already fresh in the cache, so a warm-cache cargo clippy misses these. touch src/lib.rs first to reproduce.

What

• simd_scan::find_stop: as_chunks::<16>() replaces chunks_exact(16) plus the two try_into().unwrap() casts; the tail comes from the same destructuring instead of .remainder().
• bam_dedup: as_chunks::<2>() for the (mate1, mate2) pairing.
• quant: usize::midpoint for the segment-tree split point.

Behaviour is identical: as_chunks yields the same chunks and remainder as chunks_exact, and midpoint equals (a + b) >> 1 for the non-overflowing indices here. The unsafe SIMD surface is untouched, and chunk_all_match now receives &[u8; 16] directly rather than through a checked cast.

MSRV 1.89 covers both APIs (as_chunks 1.88, usize::midpoint 1.85).

Verification

cargo clippy --all-targets -- -D warnings clean, cargo fmt --check clean, cargo test green (10 suites, 0 failures).

🤖 Generated with Claude Code