fix(python): pydantic V2 .dict calls once again use dict merging

[armandobelardo]

Fixes FER-3120

Pydantic V2 .dict calls are updated to be back to pre-3.10.4 logic.

This is fix a regression where nested literals were being omitted due to the Pydantic V2 serializers not respecting the recursive .dict logic, as Pydantic V2 shells out model_dump calls to Rust library and serializers, as opposed to recursively calling model_dump.

It is expected that performance will not be degraded given the Rust-based serializers have optimized performance, compared to the Pydantic V1 .dict approach.

I've also added onto the literal fixture to add a nested object to catch this moving forward