treewide: fix 'ruff check' errors

This is mostly about unused imports.

A couple errors remain, but are fine in my book (using `l` as a variable
name, assigning a lambda to a variable).

2019/d19/ex2/ex2.py

@@ -4,7 +4,7 @@ import sys
 from copy import deepcopy
 from dataclasses import dataclass, field
 from enum import IntEnum
-from typing import Iterator, List, NamedTuple, Tuple
+from typing import List, NamedTuple
 
 
 class ParameterMode(IntEnum):