feat: add pytest pre-commit hook and tests scaffold (issue #162)

- pyproject.toml with pytest>=8 in [dependency-groups.dev] so
  uv run --group dev pytest resolves without a global install
- tests/__init__.py and tests/conftest.py skeleton referencing issue #162
- pre-commit local hook runs pytest tests/ on Python file changes;
  exit code 5 (no tests collected) is treated as success so commits
  are not blocked while the test suite is being built out

pyproject.toml

@@ -0,0 +1,9 @@
+[project]
+name = "rpmbuilder"
+version = "0.1.0"
+requires-python = ">=3.11"
+
+[dependency-groups]
+dev = [
+    "pytest>=8",
+]