feat: support new optional sveltekit config pattern via vite config

[fubits1]

• closes 💡 Extend support for plugin SvelteKit config discovery to new Vite config option #1809
• written & tested against sveltekit@3.0.0-next.4 with pnpm (v10) & Bun
• performance diff (based on node src/cli.ts --directory fixtures/plugins/sveltekit --performance on MacBook Air M3 16GB): 68ms vs 64ms

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/knip@1810

npm i https://pkg.pr.new/@knip/language-server@1810

npm i https://pkg.pr.new/@knip/mcp@1810

commit: ba66f97

[webpro]

Thanks for the PR! Looks great, I have only a few nits I'll push now as I made the changes while playing with it already anyway.

[fubits1]

Thanks @webpro - I can confirm that the fix works!

TIL: when using Bun as package manager, the command to install from pkg.pr.new is:

bun add -d knip@https://pkg.pr.new/knip@1810