builder - cache rn project

[radoslawrolka]

📝 Description

Create caching RN project in builder for each rn_version and OS.

🎯 Type of Change

• ⚡ Performance improvement

🧪 Testing

• create cache in first build
  • workflow: https://github.com/software-mansion/rnrepo/actions/runs/21900137272
  • cache: https://github.com/software-mansion/rnrepo/actions/caches#:~:text=Linux%2Drn%2Dproject%2Dcache%2D0.80.0
• use that cache in another build
  • workflow: https://github.com/software-mansion/rnrepo/actions/runs/21900317992

[Copilot]

Pull request overview

This PR adds a React Native template project cache keyed by RN version and OS to speed up the builder workflows, and updates the builder setup logic to reuse an existing RN project directory when present.

Changes:

• Update setupReactNativeProject() to reuse an existing ${workDir}/rnrepo_build_app directory instead of erroring.
• Add actions/cache restore + “create on cache miss” steps to iOS/Android build workflows for ${{ runner.temp }}/rnrepo_build_app.
• Add a minimal validation check to ensure the cached directory looks like an RN project (package.json exists).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
packages/builder/build-utils.ts	Reuses an existing RN project directory to enable caching rather than always re-initializing.
.github/workflows/build-library-ios.yml	Restores/caches the RN project directory and creates it only on cache miss.
.github/workflows/build-library-android.yml	Same as iOS workflow: restores/caches the RN project directory and creates it only on cache miss.

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