Improve geometry file loading error handling

[Aaryan-549]

Improve geometry file loading error handling

Addresses: #1662

Summary

Adds comprehensive error handling for geometry file loading (CHEASE, FBT, EQDSK) with helpful error messages, file suggestions, and pre-parsing validation.

Problem

Geometry file loading errors were unhelpful:

• Generic FileNotFoundError without context
• Deep library stack traces obscuring the real issue
• No suggestions when files weren't found
• No validation before parsing

Solution

1. Custom Exception Hierarchy

GeometryFileError (base) ├── GeometryFileNotFoundError # with similar file suggestions ├── GeometryFileFormatError # with specific format details ├── GeometryFilePermissionError ├── GeometryFileEmptyError └── GeometryDataValidationError # for future use

2. Modular Error Handling

Created geometry_error_handling.py module with:

• find_similar_files() - Uses difflib for filename suggestions
• validate_file_access() - Pre-parsing validation

Keeps geometry_loader.py focused on core loading logic.

3. Better Error Messages

Before:

FileNotFoundError: [Errno 2] No such file or directory: 'geometry.txt' 

After:

GeometryFileNotFoundError: Geometry file not found: 'geometry.txt' Searched in directory: /path/to/geo Did you mean one of these? - geometry_file.txt - geometry_data.txt Action: Check the file path and ensure the file exists. 

4. Format-Specific Validation

• CHEASE: Header, column count, data type validation
• FBT: MATLAB structure validation
• EQDSK: COCOS parameter validation, required fields

5. Logging Integration

• INFO logs for success
• ERROR logs for failures
• EXCEPTION logs with tracebacks

Changes

New Files:

• geometry_errors.py - Exception classes
• geometry_error_handling.py - Helper functions
• tests/geometry_loader_test.py - Comprehensive tests (15+ cases)

Modified Files:

• geometry_loader.py - Enhanced with error handling

Stats: 3 files changed, 600+ insertions, 50+ deletions

Testing

• File not found with suggestions
• Permission errors
• Empty file detection
• Format errors (CHEASE, FBT, EQDSK)
• Valid file loading (regression)

Backward Compatibility

• Fully backward compatible**
• No API changes
• Only improves error messages on failures
• No performance impact on success path