Testing revamp tracking - ensuring we maintain test coverage for all the platforms we support

[fl0rek]

Tracking issue for an effort to generally improve our CI setup - speed, usability and coverage.

• Move various existing template repos into lumina and include in CI
  • Move example lumina+nextjs project into lumina repo and add CI #532
  • Move example lumina+vite project to lumina repo and add CI #533
  • Move example browser extension into lumina repo and include it in CI #534
• Browser tests in CI? Find a way to run browser tests in our CI #636
• reimplement existing rust tests for other platforms too, to raise the coverage

related #785