add require-copyright-header eslint rule

[anonrig]

I keep forgetting adding copyright headers.

[ask-bonk]

This review was generated by an AI code review assistant and may contain inaccuracies.

Adds a require-copyright-header ESLint rule to enforce Cloudflare copyright headers on all TS/JS files, and backfills 80+ files that were missing them.

• [LOW] The rule lacks auto-fix support, which would make it trivial to remediate violations on new files (see inline suggestion).

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

This PR adds a require-copyright-header ESLint rule enforced via the shared base config, and backfills 80+ files across src/cloudflare/, src/node/, src/pyodide/, and types/ that were missing the Cloudflare copyright header.

The rule implementation is correct -- the regex properly matches the expected header format (including year ranges), the base config integration is clean, and the src/node/eslint.config.mjs deduplication of the customRules plugin import is correct since it's now handled centrally.

One low-severity suggestion posted: adding fixable: 'code' + a fix() function so eslint --fix can auto-insert the header on new files, which directly addresses the "I keep forgetting" motivation.

github run

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.68%. Comparing base (fd0665d) to head (ffb16d7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6268      +/-   ##
==========================================
- Coverage   70.69%   70.68%   -0.02%     
==========================================
  Files         417      417              
  Lines      111111   111111              
  Branches    18331    18331              
==========================================
- Hits        78552    78534      -18     
- Misses      21614    21630      +16     
- Partials    10945    10947       +2     

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