Create Python tools in favour of shell scripts

Python is likely to be installed when working on Python code,
which should make it more portable and consistent.

tools/check.py

@@ -0,0 +1,22 @@
+"""
+Sort imports, format code, type-check and run offline tests.
+"""
+import subprocess
+import sys
+
+
+def run(*args: str) -> int:
+    return subprocess.run((sys.executable, "-m", *args)).returncode
+
+
+def main() -> None:
+    exit(
+        run("isort", ".", "--profile", "black", "--gitignore")
+        or run("black", ".", "--extend-exclude", r"tl/(abcs|functions|types)/\w+.py")
+        or run("mypy", "--strict", ".")
+        or run("pytest", ".", "-m", "not net")
+    )
+
+
+if __name__ == "__main__":
+    main()