usage_metadata return None in Langgraph Studio

### Checked other resources

- [x] This is a bug, not a usage question. For questions, please use GitHub Discussions.
- [x] I added a clear and detailed title that summarizes the issue.
- [x] I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example).
- [x] I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue.

### Example Code

```python
from typing import Dict, Any
from langchain_core.messages import SystemMessage
from langchain_openai import AzureChatOpenAI
from langgraph.graph import START, StateGraph, MessagesState
import os

llm = AzureChatOpenAI(
azure_deployment=os.getenv("AZURE_OPENAI_DEPLOYMENT_NAME"),
openai_api_version=os.getenv("OPENAI_API_VERSION"),
azure_endpoint=os.getenv("AZURE_OPENAI_ENDPOINT"),
temperature=0
)

# System message
system_message = SystemMessage(content="You are a helpful assistant.")

# Define the basic assistant node
def assistant(state: MessagesState) -> Dict[str, Any]:

"""Basic assistant node that processes messages."""
result = llm.invoke([system_message] + state["messages"])
print("Usage metadata: ", result.usage_metadata)
return {"messages": [result]}

# Build graph
builder = StateGraph(MessagesState)

# Add nodes
builder.add_node("assistant", assistant)

# Set entry and finish points
builder.set_entry_point("assistant")
builder.set_finish_point("assistant")

# Compile graph
graph = builder.compile()
```

### Error Message and Stack Trace (if applicable)

```shell
result.usage_metadata is None
```

### Description

When trying to access tokens usage inside the graph - always return None.
```
result = llm.invoke("hello")
print("Usage metadata: ", result.usage_metadata)
```
Usage metadata: None.

However if i use just the same code outside of langgraph (in test.py file)
```
from langchain_openai import AzureChatOpenAI
import os

llm = AzureChatOpenAI(
azure_deployment=os.getenv("AZURE_OPENAI_DEPLOYMENT_NAME"),
openai_api_version=os.getenv("OPENAI_API_VERSION"),
azure_endpoint=os.getenv("AZURE_OPENAI_ENDPOINT"),
temperature=0
)

result = llm.invoke("hello")
print(result.usage_metadata)
```
{'input_tokens': 8, 'output_tokens': 11, 'total_tokens': 19, 'input_token_details': {'audio': 0, 'cache_read': 0}, 'output_token_details': {'audio': 0, 'reasoning': 0}}

Same with llm.with_structured_output(myPydanticClass, include_raw=True) - if i use inside the langgraph information about token usage is not returned, but if i run outside - all works as expected.

Am i doing something wrong?

### System Info

System Information
------------------
> OS: Darwin
> OS Version: Darwin Kernel Version 24.0.0: Mon Aug 12 20:49:48 PDT 2024; root:xnu-11215.1.10~2/RELEASE_ARM64_T8103
> Python Version: 3.12.6 (v3.12.6:a4a2d2b0d85, Sep 6 2024, 16:08:03) [Clang 13.0.0 (clang-1300.0.29.30)]

Package Information
-------------------
> langchain_core: 0.3.46
> langchain: 0.3.21
> langchain_community: 0.3.20
> langsmith: 0.3.18
> langchain_openai: 0.3.9
> langchain_text_splitters: 0.3.7
> langgraph_api: 0.0.31
> langgraph_cli: 0.1.77
> langgraph_license: Installed. No version info available.
> langgraph_sdk: 0.1.58
> langgraph_storage: Installed. No version info available.

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
> async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
> click: 8.1.8
> cryptography: 43.0.3
> dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
> httpx: 0.28.1
> httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
> jsonpatch<2.0,>=1.33: Installed. No version info available.
> jsonschema-rs: 0.29.1
> langchain-anthropic;: Installed. No version info available.
> langchain-aws;: Installed. No version info available.
> langchain-azure-ai;: Installed. No version info available.
> langchain-cohere;: Installed. No version info available.
> langchain-community;: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.45: Installed. No version info available.
> langchain-deepseek;: Installed. No version info available.
> langchain-fireworks;: Installed. No version info available.
> langchain-google-genai;: Installed. No version info available.
> langchain-google-vertexai;: Installed. No version info available.
> langchain-groq;: Installed. No version info available.
> langchain-huggingface;: Installed. No version info available.
> langchain-mistralai;: Installed. No version info available.
> langchain-ollama;: Installed. No version info available.
> langchain-openai;: Installed. No version info available.
> langchain-text-splitters<1.0.0,>=0.3.7: Installed. No version info available.
> langchain-together;: Installed. No version info available.
> langchain-xai;: Installed. No version info available.
> langchain<1.0.0,>=0.3.21: Installed. No version info available.
> langgraph: 0.3.18
> langgraph-checkpoint: 2.0.21
> langsmith-pyo3: Installed. No version info available.
> langsmith<0.4,>=0.1.125: Installed. No version info available.
> langsmith<0.4,>=0.1.17: Installed. No version info available.
> numpy<3,>=1.26.2: Installed. No version info available.
> openai-agents: Installed. No version info available.
> openai<2.0.0,>=1.66.3: Installed. No version info available.
> opentelemetry-api: Installed. No version info available.
> opentelemetry-exporter-otlp-proto-http: Installed. No version info available.
> opentelemetry-sdk: Installed. No version info available.
> orjson: 3.10.15
> packaging: 24.2
> packaging<25,>=23.2: Installed. No version info available.
> pydantic: 2.10.6
> pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
> pydantic<3.0.0,>=2.5.2;: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4;: Installed. No version info available.
> pyjwt: 2.10.1
> pytest: Installed. No version info available.
> python-dotenv: 1.0.1
> PyYAML>=5.3: Installed. No version info available.
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> requests<3,>=2: Installed. No version info available.
> rich: Installed. No version info available.
> SQLAlchemy<3,>=1.4: Installed. No version info available.
> sse-starlette: 2.1.3
> starlette: 0.46.1
> structlog: 25.2.0
> tenacity: 9.0.0
> tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
> tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
> tiktoken<1,>=0.7: Installed. No version info available.
> typing-extensions>=4.7: Installed. No version info available.
> uvicorn: 0.34.0
> watchfiles: 1.0.4
> zstandard: 0.23.0

Start with the provided Python reproduction, comparing AzureChatOpenAI.invoke("hello") outside the graph with the assistant node invoked through graph.compile(). Check how the graph execution preserves the returned message metadata, including with_structured_output(..., include_raw=True); done means usage_metadata is available inside the graph as it is outside.

Written by the indexing model from the issue text.