Add python_git: a leak-safe GitPython alternative

Every git invocation runs through a single blocking subprocess.run
call in python_git/runner.py that always waits for the process to
exit and closes its pipes before returning, so there is no long-lived
Popen handle for a caller to forget to close (the root cause of
GitPython's known fd/process leaks).

Repo exposes status/log/diff/add/commit/push/pull/fetch, branch and
remote management, and clone, backed by dataclasses in models.py.
Covered by tests/test_repo.py, including an fd-count regression test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,15 @@
+[project]
+name = "python-git"
+version = "0.1.0"
+requires-python = ">=3.13"
+dependencies = []
+
+[dependency-groups]
+dev = ["pytest>=8.0"]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["python_git"]