feat: Add parallel test execution for multiple APIs

[kunal-yelgate]

Description

Current Behavior

Testing multiple APIs requires executing microcks test separately for each API, sequentially. With 10+ APIs in CI/CD pipelines, this becomes a significant bottleneck and wastes compute time.

Why we need this?

• Sequential testing is slow and does not scale with microservice architectures
• CI pipelines with many APIs take 5-10x longer than necessary
• No built-in way to batch or parallelize contract tests

How will this help?

• --batch + --parallel cuts CI pipeline time by 60-80%
• Worker pool pattern scales with number of APIs
• Aggregated results show pass/fail summary at a glance
• Reduces developer feedback loop from minutes to seconds

Proposed Solution

1. Create pkg/batch/batch.go for parsing batch test definitions
2. Support two input modes:
   • --batch=tests.json — JSON file with test definitions
   • --test='API1:1.0:http://api1:8080:OPEN_API_SCHEMA:30sec' — repeatable flag
3. Implement Go worker pool with sync.WaitGroup for parallel execution
4. Add --parallel flag to control concurrency (default: 1, max: 10)
5. Aggregate and report results with exit code 0 only if ALL pass

Example usage:

$ microcks test --batch=tests.json --parallel=4
Running 3 tests in parallel (max 4 workers)...
✓ API1:1.0 - PASSED (12s)
✓ API2:2.0 - PASSED (15s)
✗ API3:1.5 - FAILED (8s)

Summary: 2 passed, 1 failed
Total time: 15s (vs 45s sequential)