[Hinty] Strict equality

[gpotter2]

This issue is a reminder that we need to discuss how to handle strict equality of Mypy.

• See initial issue: Core typing: compat/config/fields/main/packet #2671 (comment)
• Mypy doc for strict equality
• discuss how to handle special cases: FlagValue...

[gpotter2]

--strict-equality is used in our typing, this is probably safe to close.