Fix lint, format and typing findings and pin dev tools

Order imports, format with ruff, make the account key constants Final
so mypy --strict accepts them, and type the test helpers. Configure
ruff and mypy in pyproject.toml and pin the dev tool versions. All
modules, classes and functions already carry Doxygen comments;
doxygen Doxyfile builds without warnings.

Task: MIL-004#2
Closes #18

tests/test_game_logic.py

@@ -58,8 +58,7 @@ def test_format_data_describes_the_account() -> None:
         "country": "United States",
     }
     assert (
-        format_data(account)
-        == "Nike, a Sportswear multinational, from United States"
+        format_data(account) == "Nike, a Sportswear multinational, from United States"
     )