Improve JSON Schema generation

We can take some notes from https://github.com/pydantic/pydantic/blob/d156ba08c140ee1e2b931120cb150080843476fe/pydantic/json_schema.py#L1064.

Maybe we can come up with an implementation that is flexible enough to support itemadapter and pydantic cases and split it into a separate library that both can reuse? Maybe learn lessons from JSON serializers out there, or even reuse one?