tests: Format all Python code with black, except tests in basics subdir.

This adds the Python files in the tests/ directory to be formatted with
./tools/codeformat.py.  The basics/ subdirectory is excluded for now so we
aren't changing too much at once.

In a few places `# fmt: off`/`# fmt: on` was used where the code had
special formatting for readability or where the test was actually testing
the specific formatting.

tests/cpydiff/modules_struct_manyargs.py

@@ -5,8 +5,9 @@ cause: Unknown
 workaround: Unknown
 """
 import struct
+
 try:
-    print(struct.pack('bb', 1, 2, 3))
-    print('Should not get here')
+    print(struct.pack("bb", 1, 2, 3))
+    print("Should not get here")
 except:
-    print('struct.error')
+    print("struct.error")