Bump actions/upload-artifact to v7 and @actions/core to 3.0.0

[Copilot]

Summary

• Bumped actions/upload-artifact from v6 to v7 in .github/workflows/check-dist.yml.
• Bumped @actions/core from ^2.0.3 to ^3.0.0 in package.json and updated package-lock.json.
• Added Jest moduleNameMapper and a local @actions/core test mock to keep tests working with @actions/core v3 ESM export conditions.

Validation

• npm install ✅
• npm run format:check ✅
• npm run lint ✅
• npm test ✅
• Parallel validation (Code Review + CodeQL) ✅ (CodeQL clean; one non-blocking review suggestion not applied)

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