Derive Hash for ThreatLevel (#186)

[octoaide]

Summary

This change adds a Hash derive for the ThreatLevel enum so it can be used directly as a HashMap key. This makes it easier for downstream crates (for example review-database) to count or group items by threat level without introducing local workarounds.

What I changed

• src/types.rs: Added Hash to the derive list for ThreatLevel.
• src/types.rs: Added test threat_level_as_hash_key that uses ThreatLevel as a HashMap key and verifies counting behavior.
• CHANGELOG.md: Added an [Unreleased] entry noting the Hash derive for ThreatLevel.

Why

Consumers of review-protocol want to use ThreatLevel in hash-based collections (e.g., HashMap) to count or aggregate events by threat level. Deriving Hash is a small, backward-compatible change that enables that usage pattern.

Notes

• Tests were added to validate ThreatLevel works as a hash key.
• Formatting/linting adjustments (if any) are incidental and not the focus of this PR.

Closes #186

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.86%. Comparing base (0412c82) to head (e2dec94).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #187      +/-   ##
==========================================
+ Coverage   85.82%   85.86%   +0.04%     
==========================================
  Files          15       15              
  Lines        6313     6331      +18     
==========================================
+ Hits         5418     5436      +18     
  Misses        895      895              

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[octoaide]

I ran the failing checks and found the cause: the test threat_level_as_hash_key referenced ThreatLevel without importing it. The test module's existing use super::*; is behind #[cfg(any(feature = "client", feature = "server"))], so when running the default cargo test / cargo clippy --tests (no features enabled) ThreatLevel ended up undeclared.

I fixed this by adding use super::ThreatLevel; directly in the test function, committed the change, and pushed it. Tests now pass and the CI checks that were blocking this PR are resolved.

Summary: added an explicit import for ThreatLevel in the failing test, pushed the fix, and CI is green.