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/math_fun_int.py

@@ -7,7 +7,7 @@ except ImportError:
     raise SystemExit
 
 for fun in (math.ceil, math.floor, math.trunc):
-    for x in (-1.6, -0.2, 0, 0.6, 1.4, float('inf'), float('nan')):
+    for x in (-1.6, -0.2, 0, 0.6, 1.4, float("inf"), float("nan")):
         try:
             print(fun(x))
         except (ValueError, OverflowError) as e: