test: kill WAL mutation survivors and update h2

[prk-Jr]

Summary

• Add focused WAL regression tests for all three reported mutation survivors:
  • new_with_replication must retain the supplied WAL configuration.
  • queued puts must retain their collection name.
  • queued deletes must retain their collection name.
• Update h2 from 0.4.13 to 0.4.16 to resolve RUSTSEC-2026-0258.
• Document the failure analysis and implementation plan.

Verification

• cargo test --workspace
• cargo test -p prkdb --lib — 202 passed
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo deny check
• cargo audit
• Final whole-branch review: no findings

The expensive cargo-mutants sweep is deferred to GitHub CI. The two new regression tests target the exact behavioral effects of all three reported survivors.