TODO: deal with typing surrounding Field.metadata while maintaining pydantic1/2 compat

[tlambert03]

there's a lot of hacks we're having to do in our internal type checking, lots of type: ignores and stuff, surrounding the metadata field in pydantic.Field ... which has been removed in favor of json_schema_extra (which isn't exactly the same thing). While we retain cross-compatibility with pydantic 1/2, might just need to keep ignoring these things. but it's something to remember