feature: Rust samples

Would be great to have some Rust samples in here.

I actually have an implementation of a pure Rust A2A client and server, if you are interested in having it.

Look at the existing samples in the repository to understand the structure and format. The issue mentions a pure Rust A2A client and server implementation; check if the contributor has shared code or details in the comments. Integrate the Rust sample by creating a new directory or notebook following the project's conventions, ensuring it demonstrates the A2A protocol usage.

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