add: .gitignore for Python project

Prevents tracking of:
- Python cache files
- Editor backups
- Test artifacts
- Temporary files

Author: miranov25

UTILS/dfextensions/groupby_regression/.gitignore

@@ -0,0 +1,36 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+
+# Testing
+.pytest_cache/
+.coverage
+htmlcov/
+.tox/
+
+# Backup files
+*.bak
+*~
+*.swp
+*.swo
+*.orig
+
+# Editor
+.vscode/
+.idea/
+*.code-workspace
+.DS_Store
+
+# Temporary
+*.tmp
+*.temp
+diff.txt
+
+# Benchmark output (optional - uncomment if you don't want results in git)
+# benchmarks/bench_out/*.json
+# benchmarks/bench_out/*.txt
+# benchmarks/bench_out/*.csv
+# benchmarks/bench_out/*.png