Make use of Bun.build's watcher

[chrisbbreuer]

Clear and concise description of the problem

We currently don't use it, and our dev script simply builds the dist folder. We could improve that.

Suggested solution

make use of Bun's watcher. Potentially also build it into our Vite plugin for a "framework maintainer" dev mode type of thing

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guide
• Check that there isn't already an issue that requests the same feature (to avoid creating a duplicate)