Add project configuration, .gitignore and the package skeleton

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

.gitignore

@@ -0,0 +1,100 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Documentation builds (Doxygen writes to build/doxygen, see Doxyfile)
+docs/_build/
+doxygen_warnings.log
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+.python-version
+
+# Environments
+.env
+.envrc
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Type checkers and linters
+.mypy_cache/
+.dmypy.json
+dmypy.json
+.pyre/
+.pytype/
+.ruff_cache/
+
+# IDEs and editors
+.idea/
+.vscode/
+*.swp
+*.swo
+.spyderproject
+.spyproject
+.ropeproject
+
+# Operating system files
+.DS_Store
+Thumbs.db
+desktop.ini

pyproject.toml

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+[build-system]
+requires = ["setuptools>=77"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "turtle-challenges"
+version = "0.1.0"
+description = "Turtle graphics exercises from Udemy's 100 Days of Code Python bootcamp (day 18)."
+readme = "README.md"
+requires-python = ">=3.13"
+license = "AGPL-3.0-only"
+license-files = ["LICENSE"]
+# Only the standard library is used at run time (turtle needs Tk, see README).
+dependencies = []
+classifiers = [
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.13",
+    "Topic :: Education",
+]
+
+[project.optional-dependencies]
+dev = [
+    "mypy>=1.13",
+    "pytest>=8.3",
+    "ruff>=0.8",
+]
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+pythonpath = ["src", "."]
+testpaths = ["tests"]
+
+[tool.ruff]
+line-length = 88
+target-version = "py313"
+src = ["src", "tests"]
+# Only the project's own code: the framework submodule and agent skills are not ours.
+include = ["src/**/*.py", "tests/**/*.py"]
+
+[tool.ruff.lint]
+select = ["ANN", "B", "E", "F", "I", "N", "SIM", "UP", "W"]
+
+[tool.mypy]
+strict = true
+files = ["src", "tests"]
+mypy_path = "src"

src/turtle_challenges/__init__.py

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+"""!
+@file __init__.py
+@brief Solutions to the turtle graphics challenges of day 18 of Udemy's
+100 Days of Code.
+
+The challenges are added one milestone at a time; see the README.
+"""

src/turtle_challenges/constants.py

@@ -0,0 +1,15 @@
+"""!
+@file constants.py
+@brief Every constant of the project, in one place.
+
+Numbers and names used by the challenges live here and nowhere else, so a
+challenge can be tuned (for example the number of dashes) without touching its
+drawing code.
+"""
+
+## Title of the turtle window.
+WINDOW_TITLE = "Turtle Challenges"
+
+## Largest value of one color channel; also the turtle color mode, so that
+## colors can be given as RGB tuples from 0 to 255.
+COLOR_MODE = 255

tests/test_package.py

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+import turtle_challenges
+from turtle_challenges import constants
+
+
+def test_package_can_be_imported_and_is_documented() -> None:
+    assert turtle_challenges.__doc__
+
+
+def test_color_mode_is_the_rgb_range_of_the_course() -> None:
+    assert constants.COLOR_MODE == 255
+
+
+def test_window_title_is_not_empty() -> None:
+    assert constants.WINDOW_TITLE