Move tests to tests/ directory and add requirements.txt

- Move test_parser.py to tests/ directory (Python best practice)
- Add requirements.txt with pytest for CI
- Update Makefile to run tests from tests/ directory
- All tests still passing locally

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: sdfsdhgjkbmnmxc

Makefile

@@ -1,5 +1,5 @@
 .PHONY: test
 
 test:
-	python -m pytest test_parser.py -v
+	python -m pytest tests/ -v
 	python -c 'import doctest, re; f = lambda: None; f.__doc__ = re.search(r"```python\n(.*?)\n```", open("README.md").read(), re.DOTALL).group(1); doctest.run_docstring_examples(f, globals(), verbose=True)'