feat: Add PySide6 GUI frontend and CLI JSON output for all diff types

Add a full PySide6-based GUI frontend (rcompare_pyside) with folder
comparison, text diff, hex diff, image diff views, dialogs, and theming.
The GUI communicates with rcompare_cli via subprocess JSON output.

Extend CLI JSON output to include text, binary, image, CSV, Excel,
JSON/YAML, and Parquet diff results alongside the existing folder scan
report. Add Serialize derives to all core diff types.

Python project uses uv for package management with hatchling build backend.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: EmanueleCannizzaro

.gitignore

@@ -89,3 +89,10 @@ cobertura.xml
 # Benchmark results
 criterion/
 bench_results/
+
+# Python
+__pycache__/
+*.py[cod]
+*.egg-info/
+.venv/
+*.egg