feat: add support for readonly persistent cache

[cellison-figma]

Summary

This adds support for a readonly option for the persistent filesystem cache. The equivalent webpack feature is documented here.

A readonly cache supports CI workflows where branch builds load in a filesystem cache from the a recent ancestor commit on the trunk branch. In many cases, these branch builds happen too often and are too ephemeral to justify storing the build cache results. Adding a readonly option allows such builds to avoid I/O costs of writing the cache to disk.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[Copilot]

Pull request overview

This PR adds support for a readonly option to the persistent filesystem cache, enabling CI workflows to load cached build artifacts from ancestor commits without incurring I/O costs of writing cache updates. This mirrors webpack's cache.readonly feature.

Changes:

• Added readonly boolean property to cache configuration types across TypeScript and Rust layers
• Modified persistent cache implementation to skip all write operations when readonly mode is enabled
• Added comprehensive end-to-end test validating that cache files remain unmodified during readonly builds

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/rspack/src/config/types.ts	Added readonly property to PersistentCacheOptions type definition
packages/rspack/src/config/normalization.ts	Added normalization logic to default readonly to false
packages/rspack/etc/core.api.md	Updated public API documentation to include readonly property
crates/rspack_binding_api/src/raw_options/raw_cache/mod.rs	Added readonly field to Rust binding options and conversion logic
crates/rspack_core/src/cache/persistent/mod.rs	Implemented readonly guards in save operations and compilation hooks
crates/rspack_core/src/cache/persistent/build_dependencies/mod.rs	Added readonly mode to skip build dependency validation
tests/e2e/cases/persistent-cache/readonly/rspack.config.js	Test configuration with readonly cache setup
tests/e2e/cases/persistent-cache/readonly/index.test.ts	E2E test verifying cache files are not modified in readonly mode
tests/e2e/cases/persistent-cache/readonly/module.js	Test module for cache validation
tests/e2e/cases/persistent-cache/readonly/index.js	Test entry point displaying module value

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[Copilot]

Corrected spelling of 'BuildDependencies' to 'Build dependencies'.

[cellison-figma]

Perhaps this tracing info is not necessary