Add mypy flags (#2472)

setup.cfg

@@ -8,6 +8,12 @@ disallow_any_generics = True
 ignore_missing_imports = True
 no_implicit_optional = True
 show_error_codes = True
+warn_unused_configs = True
+disallow_subclassing_any = True
+check_untyped_defs = True
+disallow_untyped_decorators = True
+warn_redundant_casts = True
+strict_concatenate = True
 
 [mypy-tests.*]
 disallow_untyped_defs = False