[tooling] Use optional in ImplicitDicts

[the-glu]

Fix #1221

Switch back to optional instead of | None for ImplicitDict.

Use Optional for ImplicitDict, this has two advantages:

• Autoformaters don't do modernization of the codebase as they don't see it as typing's Optional
• If ImplicitDict switch to a "better" implementation (see Do not replace Optional with | None in ImplicitDict fields #1221 comments), we can expect it to expose the new Optional here and don't have to do any change.

NB: The switch had to be done manually on the codebase, I may have miss some instances

[BenjaminPelletier]

Oof, thanks for biting the bullet on making these changes semi-manually