feat: bring lazy platform compilation to Rspack

[jbroma]

Summary

Bring the Rspack development experience to parity with Webpack by compiling each configured platform only when its bundle is first requested.

Developer wins

• The development server starts without eagerly compiling every configured platform.
• Launching an iOS app no longer waits for an unused Android build, and vice versa.
• Each platform keeps independent compilation state, progress reporting, HMR notifications, stats, and asset caching.
• A platform compiles once on first request, then serves subsequent bundle requests from the existing cache until a source change triggers a rebuild.
• Shutdown now closes Rspack cleanly, rejects pending bundle requests, and still stops the development server when compiler shutdown fails.

How it works

Rspack starts every child compiler in a multi-compiler eagerly. Re.Pack now holds each child compiler at its initial watch run and releases it on the first bundle request for that platform. The watcher timestamps are refreshed when a gate is released to prevent the deferred compiler from treating changes made during startup as a second, phantom rebuild.

Unsupported platforms fail immediately instead of leaving requests pending. The implementation also tracks compilation, assets, stats, and request resolvers per platform.

Validation

• Focused lazy-compilation compiler tests: 5/5 passed
• Tester app dev-server integration tests: 2/2 passed
• Re.Pack TypeScript and Biome checks passed
• iOS smoke test passed
• Watcher behavior verified with Rspack 1.6, 2.0, and 2.1
• Changeset validation passed

[changeset-bot]

🦋 Changeset detected

Latest commit: b5e84c5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@callstack/repack	Minor
@callstack/repack-plugin-expo-modules	Minor
@callstack/repack-plugin-nativewind	Minor
@callstack/repack-plugin-reanimated	Minor
@callstack/repack-dev-server	Minor
@callstack/repack-init	Minor

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