Extra fields from custom AgentState not available during streaming

[Iamsdt]

When defining a custom AgentState, the additional fields are not accessible during streaming updates.
Minimal reproducible example:

class MyAgentState(AgentState):
    cv_text: str = ""
    cid: str = ""
    jd_text: str = ""
    jd_id: str = ""

During agent execution, when using streaming responses, only the default fields are included.
The custom fields (cv_text, cid, jd_text, jd_id) do not appear in the streamed state updates.

Expected Behavior

• All fields declared in the custom AgentState should be included in the streaming payload.
• The streaming state should fully reflect the extended model.

Actual Behavior

• While running the agent with streaming enabled:

  • Custom fields are missing.
  • Only the base AgentState fields are streamed.

Why This Matters

These custom fields are required for:

• Reference data through the agent lifecycle
• Debugging and introspection
• Downstream consumers relying on full state in streaming mode

Steps to Reproduce

1. Create a custom AgentState with extra fields.
2. Run an agent with streaming enabled.
3. Inspect streamed events → the extra fields are not included.

[Iamsdt]

Fixied with this pr: #13