Use tsdown for building the library

[timokoessler]

• Would allow us to bundle dependencies, e.g. unplugin, to ensure we still have 0 npm dependencies
• Reduce lib size & loading time

Todos

• Some benchmarks are trying to import internal files from the build directory
• Rolldown does not work on old Node.js versions

Summary by Aikido

Security Issues: 0	Quality Issues: 0	Resolved Issues: 0

⚡ Enhancements

• Switched library build to tsdown and updated build scripts
• Adjusted CI to produce original and flattened build artifacts
• Changed build output handling and added d.ts imports // @ts-ignore

🔧 Refactors

• Introduced getLibraryRoot and isLibBundled and replaced hardcoded paths
• Updated ESM test script to require Node 24 and async parsing

^{More info}

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
library/helpers/getLibraryRoot.ts	75.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!