Optimize CI/CD: Optimize if-nodejs-pr-testing.yml to reduce CI time

## Problem

The centrally managed `if-nodejs-pr-testing.yml` workflow is missing several standard optimizations that would significantly reduce CI time across all AsyncAPI repositories.

### Proposed Changes

1. Add Concurrency Control

2. Add Path Filtering

3. Skip Merge Commits

4. Enable NPM Caching

I’m happy to submit a PR implementing this.

Start with the centrally managed if-nodejs-pr-testing.yml workflow and inspect how pull requests currently trigger it. Review the existing configuration before adding concurrency control, path filtering, merge-commit skipping, and NPM caching. Done means all four optimizations are configured and the workflow still runs correctly with reduced CI time.

Written by the indexing model from the issue text.