GitHub Actions workflow optimization needed

[catherinevee]

The current CI pipeline takes 15+ minutes to complete, mainly due to:

• Sequential test execution
• No caching of Go modules between runs
• Building for all platforms even for PRs
• No parallelization of linting and testing

Proposed optimizations:

1. Add matrix strategy for parallel testing
2. Implement proper Go module caching
3. Only build current platform for PRs
4. Run linting and testing in parallel

This would reduce CI time to under 5 minutes.