[Lake][Subgraph] Clean up subgraph objects, use pydantic table objects instead.

[idiom-bytes]

Background / motivation

Subgraph objects (Prediction, Slot, Payout, Subscription) are unnecessary and redundant.

Subgraph fetching is part of data-integration, the flow should be:

1. to validate it
2. save it to CSV
3. add to duckdb-lake

Perhaps, make sure that pydantic update is in place - #973

TODOs / DoD

• [ ] Remove redundant data objects inside subgraph
• [ ] Utilize pydantic objects for validating data coming from subgraph
• [ ] Update tests or anywhere else as required

[calina-c]

@idiom-bytes I think this can be closed, right?

[idiom-bytes]

Yes it can, closing...