Optimize diff generation and add transitive dependency toggle

[stixx]

✨ Key Changes

• Direct Dependency Filtering (Default): The action now defaults to reporting only changes in direct dependencies. This significantly reduces "noise" from transitive updates and prevents exceeding GitHub's 64KB comment limit.
• New Toggle: Added include-transitive input. Set it to true if you still need to see every sub-dependency change.
• Improved Reliability:
  • Increased Git maxBuffer to 50MB to prevent crashes on massive package-lock.json files.
  • Added helpful error messaging for shallow clones (reminding users to set fetch-depth: 0).
• Fixed NPM Links: Resolved issues where nested packages generated broken 404 links to the npm registry.