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/float/builtin_float_minmax.py

@@ -29,4 +29,3 @@ print(min([1, 2.9, 4, 6.5, -1, 2]))
 print(max([1, 2.9, 4, 6.5, -1, 2]))
 print(min([1, 2.9, 4, -6.5, -1, 2]))
 print(max([1, 2.9, 4, -6.5, -1, 2]))
-