Allow to pass to .invoke method {messages: list[AnyMessage}

### Checked other resources - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [x] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs _No response_ ### Reproduction Steps / Example Code (Python) ```python from langchain.agents import create_agent from langgraph.graph.message import MessagesState # Create full agent agent = create_agent(model="openai:gpt-4o-mini", system_prompt="You are a personalized assistant. Just say hi.") agent.invoke(MessagesState(messages=[HumanMessage(content="What's your name?")])) ``` ### Error Message and Stack Trace (if applicable) ```shell Argument of type "MessagesState" cannot be assigned to parameter "input" of type "_InputAgentState | Command[Unknown] | None" in function "invoke" Type "MessagesState" is not assignable to type "_InputAgentState | Command[Unknown] | None" "messages" is an incompatible type "list[AnyMessage]" is not assignable to "list[AnyMessage | dict[str, Any]]" "MessagesState" is not as…