Agent does not implement stream

[samuelint]

Is your feature request related to a problem? Please describe.
Agent does not implement stream. Got error stream not implemented for this chain.
https://github.com/Abraxas-365/langchain-rust/blob/891c56f0e2f2a98eed883f906c3de6cb82770797/src/agent/executor.rs
This is making agents almost useless, streaming is an important feature for UX experience.

Describe the solution you'd like
Agent streaming to be implemented.

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I can definitely contribute and implement it. Before, is there anything I should know about this use case? Is there any difficulties I might not be aware of?

Thanks