feat: experimental rolldown support

[pi0]

This PR adds experimental support for rolldown bundler (for development and production nitro Builds) as a faster alternative to rollup.

In the next steps, we will add Vite support as a bundler as well (which allows using either vite as a standalone bundler or using Nitro as an environment build target for Vite).

Supporting both rolldown and vite is easy in the long term as both 3 share a common rollup plugin API.

This feature will be available initially on nitro-nightly channel and can be opted in using builder: "rolldown" config or NITRO_BUILDER=rolldown environment variable + installing rolldown peer dependency.

It is likely that all 3 rolldown, vite, and rollup become optional peer dependencies of Nitro so users can choose.

/cc @yyx990803 @hyf0 @IWANABETHATGUY @underfin @Boshen @shulaoda @sapphi-red

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Current failing tests: (4/39)

pnpm test:rolldown test/presets/node.test.ts

• JSX support (there is no neutral option to avoid react)
• Static build flags (import.meta.dev, etc) plugin fails
• Raw loader (rolldown wrongly processes \0path\to\asset.json and fails)
• Externals bundled
• Async context

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[pi0]

(merging to iterate faster on v3 branch. feedbacks and contributions are more than welcome 🙏🏼 )