Added sample protobuf services math_server and math_client

[genevanmeter]

Summary

Adds a rust version of the ecal main repo's math_server and math_client which uses protobuf rpc message definitions.

I was looking to use ecal services with protobuf like we do in our python ecal codebase and didn't see any examples. I first attempted to create a new TypedService that mirrored TypedPublisher/Subscriber but was getting stuck. This is a simple implementation that expects the developer to know that they using protobufs types on both the server and client.

Checklist

• I have tested this change locally
• [N/A ] I have documented any public APIs or CLI changes
• I have added appropriate examples or comments
• The code builds and passes all checks (cargo check, cargo test)
• [N/A] I have updated the changelog if applicable

Run
cargo run --bin math_server
cargo run --bin math_client

Compatible with the ecal provided ecal_sample_math_server and ecal_sample_math_client