Streamline and simplify the fallback logic

requestIdleCallback is no longer used, since its implementation was a misuse.

Whenever the Scheduler API is not supported, use a delayed callback: this aligns the behaviour on Node.js to a browser with a fallback, since the exception for Node was not justified.
When the priority is user-blocking and the Scheduler is not supported,
queue a microtask where possible.

Update `.npmignore`

The npm package accidentally included the YAML for GitHub Actions. It is now ignored.

Add provenance

Update some documentation and configure the provenance publication on npm

Add types

Patch the package and include a TypeScript declaration for the entrypoint.

Main release

Publish the package openly on GitHub and on npm.