feat: Enable dynamic toggling of tool choice in v3 agent loop for OpenAI [LET-4564] (#5042)

* Add subsequent flag

* Finish integrating constrained/unconstrained toggling on v3 agent loop

* Update tests to run on v3

* Run lint

letta/llm_api/google_vertex_client.py

@@ -280,6 +280,7 @@ class GoogleVertexClient(LLMClientBase):
         llm_config: LLMConfig,
         tools: List[dict],
         force_tool_call: Optional[str] = None,
+        requires_subsequent_tool_call: bool = False,
     ) -> dict:
         """
         Constructs a request object in the expected data format for this client.