Add comprehensive error handling to image lifecycle

[chorrell]

Summary

Adds robust error handling to image build and cleanup operations to prevent resource leaks and provide better visibility into failures.

Changes

In create_image:

• ✅ Catch Docker build failures with clear error messages
• ✅ Re-raise exceptions appropriately to fail tests
• ✅ Provides context when builds fail

In delete_image:

• ✅ Guard against nil @image (if build never completed)
• ✅ Wrap container cleanup in error handling
• ✅ Continue cleanup even if individual containers fail
• ✅ Handle NotFoundError if image already removed
• ✅ Always attempt image removal even if container cleanup fails
• ✅ Add informative status messages

Problem Solved

Before: If Docker image build failed, cleanup would crash trying to remove a nil image. If container cleanup failed, image removal would be skipped, leaving dangling images.

After: Cleanup is resilient and continues even when errors occur, preventing resource leaks.

Benefits

✅ Graceful failures - Clear error messages when builds fail
✅ Prevents resource leaks - Cleanup attempts even after failures
✅ Better debugging - Status messages show what's happening
✅ Resilient cleanup - Individual failures don't prevent overall cleanup

Testing

✅ All existing tests pass with new error handling
✅ Verified delete_image handles nil @image safely
✅ Cleanup messages appear in test output
✅ No behavioral changes for successful test runs