feat: Verify strict equality

See
<https://mypy.readthedocs.io/en/latest/command_line.html#cmdoption-mypy-strict-equality>.

Author: l0b0

mypy.ini

@@ -8,6 +8,7 @@ disallow_untyped_defs = True
 ignore_missing_imports = True
 no_implicit_optional = True
 show_error_codes = True
+strict_equality = True
 warn_redundant_casts = True
 warn_return_any = True
 warn_unused_ignores = True