The drawing functions take a Pen, the part of turtle.Turtle they use, so a test can
pass a fake that records every call. window.py is the only module that imports
turtle, and it does so inside the functions so that importing the package needs no Tk.
Task: MIL-002#1
Task: MIL-002#2
pyproject.toml declares Python 3.13 or later, an empty runtime dependency list and
pytest, ruff and mypy as development tools. The package has constants.py, the one
place for constants, and a smoke test keeps the test run green.
Task: MIL-001#1
Task: MIL-001#2
Task: MIL-001#3