[RFC] Custom Serialization in @traceable

[hinthornw]

Some options:

1. Via a process_inputs callback in the decorator itself
2. my_arg: Annotated[List, my_serialization_fn]
3. Use pydantic (not currently a dep) my_arg: Annotated[List, WrappedSerializer(my_serialization-fn]

Leaning towards a variant of (2). Probably have something like

from typing_extensions import Annotated
from langsmith import Serializer

@traceable
def foo(x: Annotated[MyObject, Serializer(my_func)]) -> str:
      return ....

Could extend do have some defaults like hiding, etc.

from typing_extensions import Annotated, Hide
from langsmith import Serializer

@traceable
def foo(x: Annotated[MyObject, Serializer(my_func)], my_secret: Annotated[str, Hide()]) -> str:
      return ....

[hinthornw]

And the crowd goes wild