[wrapper] Remove rxjs from @notemine/wrapper, add @notemine/rxjs package instead

[dskvr]

Will be more performant, and easier to integrate client-side frameworks and easier for implementers, if observables aren't included in the wrapper package.

• Remove observables logic and rxjx from @notemine/wrapper
• Add hooks for handling messages.
• Add @notemine/rxjs package with a library that extends @notemine/wrapper
• Add @notemine/svelte5 package with a library that extends @notemine/wrapper and has component exports
• Update svelte demo
• Create rxjs-demo that is based on vanilla-js-demo but uses @notemine/rxjs instead of @notemine/core artifacts.