feat(rsc): ability to preserve decoded server references

[james-elicx]

Extracts the core, React, and server-manifest reference-preservation changes from #1246.

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RSC frameworks may need to cache, proxy, or compose Flight fragments before sending them back to the browser. A concrete example is a use cache wrapper that stores a rendered product card as a Flight stream and later replays it into a new RSC response.

That cached fragment can still contain a server action, like an “add to cart” action owned by the framework/runtime. During replay, the cache layer should not have to import the action implementation from the app bundler manifest; it only needs to keep the action reference opaque so the browser can call it through the normal action path later.

This adds an opt-in serverReferences: "preserve" decode mode for that case. It also preserves and deduplicates server-reference export names when transforms share a module, and adds an experimental serverReferenceMarkers option so preceding transforms can mark modules whose server-reference metadata must survive the "use server" HMR cleanup pass.

The e2e caches a Flight stream containing a framework-owned server action reference, replays that cached stream, and verifies the replayed client UI can still invoke the action.