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/feature_check/float.py

@@ -5,9 +5,9 @@ try:
 except NameError:
     print(0)
 else:
-    if float('1.0000001') == float('1.0'):
+    if float("1.0000001") == float("1.0"):
         print(30)
-    elif float('1e300') == float('inf'):
+    elif float("1e300") == float("inf"):
         print(32)
     else:
         print(64)