feat: hmr integration

[florian-lefebvre]

While investigating HMR support for the integration template, I found out it was fairly easy. It just requires a few changes here:

• new hmrIntegration
• renamed watchIntegration to watchDirectory

TODO:

• [x] package
  • [x] rename watchIntegration to watchDirectory
  • [x] write hmrIntegration
• [x] tests
• [x] playground
  • [x] use hmrIntegration + dynamic import
• [x] docs
  • [x] rename watchIntegration to watchDirectory
  • [x] breaking changes
  • [x] new dev section for hmrIntegration
  • [x] update sidebar (links + badges)
• [x] changeset
• [x] lint

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