refactor(group,dedup): reduce duplication and remove dead code

[nh13]

Summary

• Replace local TagFamilySizeMetric struct in group.rs with FamilySizeMetrics from fgumi-metrics (dedup.rs already used this)
• Add FamilySizeMetrics::from_size_counts() to centralize the histogram computation that was duplicated verbatim in both group.rs and dedup.rs
• Remove dead _assign_tag_bytes parameter that was threaded through 3 functions but never used (tags are set during serialization)
• Remove unused serde import

Test plan

• All 1838 tests pass (cargo ci-test)
• Formatting clean (cargo ci-fmt)
• Linting clean (cargo ci-lint)
• New unit tests for FamilySizeMetrics::from_size_counts() (normal + empty cases)

[coderabbitai]

Warning

Rate limit exceeded

@nh13 has exceeded the limit for the number of commits that can be reviewed per hour. Please wait 1 minutes and 35 seconds before requesting another review.

⌛ How to resolve this issue?

After the wait time has elapsed, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

We recommend that you space out your commits to avoid hitting the rate limit.

🚦 How do rate limits work?

CodeRabbit enforces hourly rate limits for each developer per organization.

Our paid plans have higher rate limits than the trial, open-source and free plans. In all cases, we re-allow further reviews after a brief timeout.

Please see our FAQ for further information.

📥 Commits

Reviewing files that changed from the base of the PR and between 3a460ea and d1417be.

📒 Files selected for processing (3)

• crates/fgumi-metrics/src/group.rs
• src/commands/dedup.rs
• src/commands/group.rs

✨ Finishing Touches

🧪 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-commands-umi-group

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.62%. Comparing base (3a460ea) to head (d1417be).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
src/commands/dedup.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #153      +/-   ##
==========================================
+ Coverage   83.61%   83.62%   +0.01%     
==========================================
  Files         126      126              
  Lines       51510    51475      -35     
==========================================
- Hits        43069    43048      -21     
+ Misses       8441     8427      -14     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.