@actions/cache: convert to an ESM module

[danwkennedy]

Description

We're converting all packages in this repo to ESM modules. @actions/cache is one of leaf packages and can be converted now.

[Copilot]

Pull request overview

This PR converts the @actions/cache package from CommonJS to ESM-only, marking it as a major breaking change with version 6.0.0. The conversion aligns with the broader ESM migration across the GitHub Actions toolkit packages.

Changes:

• Package converted to ESM with "type": "module" and exports configuration
• TypeScript configured for ESM output with module: "node16" and moduleResolution: "node16"
• All relative imports updated with .js extensions for ESM compatibility
• Dependencies upgraded to ESM-compatible versions (@actions/core 3.0.0, @actions/exec 3.0.0, etc.)
• Created package-version.cjs CommonJS wrapper to read package.json version in ESM context
• Removed direct dependency on @azure/abort-controller in favor of global AbortController (Node.js 18+)
• Jest configuration updated to handle ESM cache module

Reviewed changes

Copilot reviewed 13 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/cache/package.json	Updated to version 6.0.0, added ESM configuration, upgraded dependencies to latest ESM-compatible versions, updated build script
packages/cache/tsconfig.json	Added ESM module settings (node16) for proper module resolution
packages/cache/src/cache.ts	Updated all relative imports to include .js extensions
packages/cache/src/internal/*.ts	Updated all relative imports to include .js extensions across all internal modules
packages/cache/src/internal/shared/user-agent.ts	Refactored to import version from new package-version.cjs file
packages/cache/src/internal/shared/package-version.cjs	New CommonJS module to provide package version to ESM modules
packages/cache/src/generated/**/*.ts	Updated generated protobuf code with .js extensions in relative imports
packages/cache/package-lock.json	Updated all dependency versions consistently with package.json changes
packages/cache/RELEASES.md	Added 6.0.0 release notes documenting ESM-only breaking change
jest.config.js	Added @actions/cache module mapping and transform patterns for ESM testing

Files not reviewed (1)

• packages/cache/package-lock.json: Language not supported

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.