Use Vite

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Has HMR support:
https://github.com/crxjs/chrome-extension-tools

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Used this on a personal project and while it was awesome for HMR it was awfully slow for cold starts, taking around 60s to build. Need to see if can fix that somehow.

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The beta versions of [vite, @crxjs/vite-plugin, @vitejs/plugin-react] seem to run much faster, taking only around 15s to build on a cold start. It requires setting "type": "module" to use esm which may be problematic.

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@vitejs/plugin-react-swc is even faster again