fix(vite): set ssr.noExternal even if not in project package.json

[mcous]

If @testing-library/svelte is not set in the package.json of the project Vitest is running in (e.g. in certain monorepo setups), @sveltejs/vite-plugin-svelte will not detect that it needs to be inlined. This, in turn, breaks Svelte 5 support, which relies on STL running through the Svelte compiler for runes support.

Hopefully this is something that can be fixed in @sveltejs/vite-plugin-svelte, but it might not be! This PR updates our own Vite plugin to ensure this setting is correct, even if @sveltejs/vite-plugin-svelte misses it.

Fixes #403

[mcous]

Setup file has issues in the same monorepo setup this PR sets out to address, see playerfine/svelte5unittestingexample#1 (comment)

TODO

• Disable auto cleanup if Vitest is in globals mode
• Figure out why cleanup setupFiles addition fails in a monorepo, adjust as necessary
  • Cause: misconfiguration in example monorepo, Vitest and plugin behaving as expected

[github-actions]

🎉 This PR is included in version 5.2.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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