build: migrate from rollup to tsdown

[remarkablemark]

What is the motivation for this pull request?

Refactor the package build from Rollup to tsdown while preserving the existing published module layout, and remove the now-unused dist/htmlparser2.js browser bundle.

What is the current behavior?

The package build is orchestrated through Rollup plus shell/codemod helpers, including a source-mutating ESM build flow. The build also emits dist/htmlparser2.js, which is no longer used by the current test suite.

What is the new behavior?

The package now builds through tsdown with explicit CJS, ESM, and UMD targets. The Rollup config and helper scripts are removed, the ESM smoke test is kept under __tests__/esm, ESLint/TS config is adjusted for the new bundler config file, and dist/htmlparser2.js is no longer produced.

plan.md

Checklist:

• Conventional Commits
• Tests
• Types
• Documentation

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
dist/html-dom-parser.min.js	2.18 KB (-5.03% 🔽)	44 ms (-5.03% 🔽)	93 ms (+56.24% 🔺)	136 ms

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (3a3929c) to head (ed823cb).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1469   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          122       122           
  Branches        31        31           
=========================================
  Hits           122       122           

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