feat: bundle in CJS and ESM formats

[Belco90]

Checks

• I have read the contributing guidelines.

Changes

• Set up a bundler (tsdown)
• Update package.json fields for CJS and ESM exposed files
• Set up publint for linting the published bundle
• Replace CJS imports and exports with ESM equivalents
• Update type to "module"
• Move remaining .cjs to ESM format
• Rename lib/ to src/
• Adjust types (mirroring eslint-plugin-vitest and using eslint exported types)
• Use eslint-doc-generator --check within generate-all:check script

Context

Closes #900

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.39%. Comparing base (3cc095b) to head (5bc13f0).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1130      +/-   ##
==========================================
- Coverage   97.40%   97.39%   -0.02%     
==========================================
  Files          48       48              
  Lines        5826     5803      -23     
  Branches     1477     1477              
==========================================
- Hits         5675     5652      -23     
  Misses        149      149              
  Partials        2        2              

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