feat(codecov): setup checks

[avivkeller]

@nodejs/web-infra Please set codecov/patch, codecov/project, CI / Tests & Coverage and CI / Lint & Format as required checks.

Ref: #305

[Copilot]

Pull Request Overview

Adds a Codecov configuration to enforce coverage thresholds on pull requests and the overall project.

• Introduces codecov.yml with patch and project coverage status targets
• Includes TODOs for raising thresholds once coverage improves

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.90%. Comparing base (42bbad6) to head (c22f9f1).
Report is 3 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #306      +/-   ##
==========================================
+ Coverage   41.24%   48.90%   +7.66%     
==========================================
  Files          94       82      -12     
  Lines        7092     6825     -267     
  Branches      211      277      +66     
==========================================
+ Hits         2925     3338     +413     
+ Misses       4164     3484     -680     
  Partials        3        3              

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🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[avivkeller]

Ref: https://github.com/nodejs/api-docs-tooling/pull/306/checks?check_run_id=43487952781
Ref: https://github.com/nodejs/api-docs-tooling/pull/306/checks?check_run_id=43487953618

[avivkeller]

This shouldn't land until #307, plus the followup which will get us from 40-ish to 43-ish (so we have a bit of margin)

[AugustinMauroy]

bump @avivkeller Linting is failing 😃