Add batch server logging

[jonhealy1]

• Intelligent Batch Logging: Enhanced the /validate endpoint with high-visibility logging for both single-item and bulk ItemCollection requests.
• Error Aggregation: Implemented a frequency-based error summarizer for large batches. Instead of flooding logs, the service now identifies and counts unique failure reasons (e.g., "Top failure reason (99/100): 'datetime' is required").
• Schema Contextualization: Validation failures now include the specific AbsoluteKeywordLocation, allowing developers to click directly to the failing STAC Extension schema.
• Performance Metrics: Real-time execution timing added to all validation logs to monitor throughput and latency.
• Project Tooling: Added a Makefile and go test suite to standardize the contributor workflow and ensure build stability.