fix: return the same instance of ModuleNode for the same EnvironmentModuleNode

[sapphi-red]

Description

This PR should fix the vite-plugin-svelte fail (https://github.com/vitejs/vite-ecosystem-ci/actions/runs/11473350317/job/31927446107) by improving backward compat of the ModuleGraph.

It was failing because this inline_styles function never resolved.
https://github.com/sveltejs/kit/blob/dcbe4222a194c5f90cfc0fc020cf065f7a4e4c46/packages/kit/src/exports/vite/dev/index.js#L189-L194
This find_deps function was recursively called infinitely because moduleGraph.getModuleByUrl returned a new instance for the same ModuleNode.
https://github.com/sveltejs/kit/blob/dcbe4222a194c5f90cfc0fc020cf065f7a4e4c46/packages/kit/src/exports/vite/dev/index.js#L578-L614
This PR prevents that happening by caching the ModuleNode.

[sapphi-red]

Due to the simplicity of this implementation, a memory leak occurs in one particular case.

const dualWeakMap = new DualWeakMap()
const k1 = {}
const k2 = {}
dualWeakMap.set(k1, k2)
//
// some time passes and k2 gets dropped from memory, but k1 was kept
//

// this should return false because there's no entries in `dualWeakMap.map.get(k1)`
// but this return true
// since this implementation does not remove the inner map when the entry in the inner map is dropped
dualWeakMap.map.has(k1)

But I think this is fine for our case. Modules doesn't get dropped usually, and I assume the memory size of an empty Map is not that big.

[bluwy]

Yeah I think it should be fine too. If k2 (which refers to the ssrModule) gets dropped and k1 (the clientModule) still exists, then I think it'll at least be cached with the clientModule + undefinedKey pair so the weakmap is still useful.

The tricky part I guess is that undefinedKey would always exist which would cause the memory leak.

[sapphi-red]

/ecosystem-ci run

[vite-ecosystem-ci]

📝 Ran ecosystem CI on c17b6aa: Open

suite	result	latest scheduled
astro	❌ failure	❌ failure
nuxt	❌ failure	✅ success
redwoodjs	❌ failure	❌ failure
remix	❌ failure	❌ failure
sveltekit	❌ failure	❌ failure
vike	❌ failure	❌ failure
vite-plugin-svelte	✅ success	❌ failure
vitest	❌ failure	❌ failure

✅ analogjs, histoire, ladle, laravel, marko, previewjs, quasar, qwik, rakkas, storybook, unocss, vite-environment-examples, vite-plugin-pwa, vite-plugin-react, vite-plugin-react-swc, vite-plugin-vue, vite-setup-catalogue, vitepress, vuepress

[sapphi-red]

nuxt fails with main branch too (ran locally).

[patak-dev]

Uh, nice one Sapphi! This is a very interesting approach. Hopefully we'll see the ecosystem move away from server.moduleGraph so we can forget this file ever existed at one point.