test: increase code coverage from 74% to 98%

Add comprehensive tests for all modules:
- xml_editor.py: error handling, utility functions, edge cases
- track_changes.py: revision parsing, accept/reject operations
- comments.py: comment operations, error handling
- workspace.py: sync checks, error paths
- document.py: settings updates, relationship handling
- ooxml/pack.py and unpack.py: error cases

Mark LibreOffice validation code as pragma: no cover since it
requires external tools not available in CI.

Author: pablospe

.gitignore

@@ -54,6 +54,7 @@ coverage.xml
 .hypothesis/
 .pytest_cache/
 cover/
+tests/test_data/.docx
 
 # Translations
 *.mo

docx_editor/ooxml/pack.py

@@ -50,15 +50,15 @@ def pack_document(input_dir: str | Path, output_file: str | Path, validate: bool
                     zf.write(f, f.relative_to(temp_content_dir))
 
         # Validate if requested
-        if validate:
+        if validate:  # pragma: no cover
             if not validate_document(output_file):
                 output_file.unlink()  # Delete the corrupt file
                 return False
 
     return True
 
 
-def validate_document(doc_path: Path) -> bool:
+def validate_document(doc_path: Path) -> bool:  # pragma: no cover
     """Validate document by converting to HTML with soffice."""
     # Determine the correct filter based on file extension
     match doc_path.suffix.lower():