[Feature] Improve URDF model loading error messages and diagnostics

[strangerwhoisharborofdoom]

When loading URDF models that fail to parse, gz-physics sometimes produces cryptic error messages that don't help users identify the root cause.

Problem

Error messages like Failed to load model without specific details about:

• Which URDF element caused the failure
• Line number or element path in the URDF
• Whether it's a link, joint, collision, or visual element

Suggested Improvement

Enhance error reporting to include:

1. The specific URDF element name/path that failed
2. A brief hint about what might be wrong
3. Line/column references where applicable

This would significantly reduce debugging time for users working with robot models in Gazebo. Happy to contribute if this is a welcome improvement.