OK let's do this for every remaining python file

Author: multiplemonomials

tools/python/mbed_tools/build/_internal/config/assemble_build_config.py

@@ -4,6 +4,8 @@
 #
 """Configuration assembly algorithm."""
 
+from __future__ import annotations
+
 import itertools
 import logging
 

tools/python/mbed_tools/build/_internal/find_files.py

@@ -4,7 +4,8 @@
 #
 """Find files in MbedOS program directory."""
 
-import fnmatch
+from __future__ import annotations
+
 from pathlib import Path
 from typing import Callable, Iterable, List, Optional, Tuple
 

tools/python/mbed_tools/build/config.py

@@ -4,7 +4,8 @@
 #
 """Parses the Mbed configuration system and generates a CMake config script."""
 
-import json
+from __future__ import annotations
+
 import pathlib
 from typing import Any, Tuple
 import logging