fix: transform lists, iterables, and sequences

[kenany]

This is convenient for users that are doing something like this:

class PangeaMessage(BaseModel):
    model_config = ConfigDict(extra="forbid")

    role: Optional[str] = None
    content: str

# ...

guard_input_response = client.guard_chat_completions(
    guard_input={"messages": [PangeaMessage(role="user", content="hello"), ...]}, event_type="input"
)