initial impl

tests/test_line_limits.py

@@ -0,0 +1,13 @@
+from pathlib import Path
+
+
+def test_python_files_are_at_most_250_lines() -> None:
+    root = Path(__file__).parents[1]
+    files = [*root.glob("src/**/*.py"), *root.glob("tests/**/*.py")]
+    oversized = {
+        str(path.relative_to(root)): len(path.read_text().splitlines())
+        for path in files
+        if len(path.read_text().splitlines()) > 250
+    }
+    assert oversized == {}
+