call FlowRunContext.model_rebuild() in hydrate_context

[zzstoatzz]

fixes EngineContext rebuild error, which when occurring was causing this downstream error, as the pydantic error could not be serialized

ray.exceptions.RaySystemError: System error: Failed to unpickle serialized exception
traceback: Traceback (most recent call last):
  File "/Users/nate/Library/Caches/uv/archive-v0/9aF8mmPcr6WgOvDDdAgDC/lib/python3.12/site-packages/ray/exceptions.py", line 51, in from_ray_exception
    return pickle.loads(ray_exception.serialized_exception)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: PydanticErrorMixin.__init__() missing 1 required keyword-only argument: 'code'

and assorted typing improvements

[codspeed-hq]

CodSpeed Performance Report

Merging #16628 will not alter performance

_{Comparing prefect-ray-fixes (d50e605) with main (fbffa5c)}

Summary

✅ 3 untouched benchmarks

[zzstoatzz]

open to better ways to do this (if possible)

[desertaxle]

I think only Flow is needed for this rebuild, so it might be worthwhile only to import Flow and pass it into _types_namespace.

[zzstoatzz]

that's what I expected as well, and did at first, but unfortunately that doesn't fix the problem. we see the same unpickleable error

[desertaxle]

Hmm, well if we're importing _types, we might as well just import prefect.main which would allow us to remove the explicit model_rebuild call here.

[aaazzam]

and the circle continues