refactor(metrics): consolidate UmiCountTracker and remove ALL_REJECTIONS duplication

[nh13]

Summary

• Consolidate UmiCountTracker from 3 separate HashMaps (raw counts, error counts, unique counts) into a single HashMap<String, (usize, usize, usize)>, eliminating redundant key cloning on each record() call
• Replace ALL_REJECTIONS const array (which manually listed CORE + OPTIONAL rejections) with all_rejections() function that chains the two source arrays

Test plan

• cargo nextest run -p fgumi-metrics — all tests pass
• cargo ci-fmt — clean
• cargo ci-lint — clean

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 3a460ea and 376a6d6.

📒 Files selected for processing (2)

• crates/fgumi-metrics/src/consensus.rs
• crates/fgumi-metrics/src/duplex.rs

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📝 Walkthrough

Walkthrough

This pull request refactors internal data structures in the metrics crate. The consensus module replaces a static ALL_REJECTIONS array with a private function that dynamically chains core and optional rejection arrays. The duplex module consolidates three separate per-UMI counter maps into a single map with tuple values. Both changes maintain existing public APIs while simplifying internal implementation and reducing code duplication.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title accurately summarizes both main changes: consolidating UmiCountTracker and removing ALL_REJECTIONS duplication.
Description check	✅ Passed	Description clearly relates to the changeset, detailing both refactoring efforts and including a comprehensive test plan.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch refactor/nh/simplify-fgumi-metrics

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.61%. Comparing base (3a460ea) to head (376a6d6).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #145   +/-   ##
=======================================
  Coverage   83.61%   83.61%           
=======================================
  Files         126      126           
  Lines       51510    51510           
=======================================
  Hits        43069    43069           
  Misses       8441     8441           

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[nh13]

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[nh13]

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