Implement gRPC Communication

Implement gRPC-based communication between the Gateway and Endorser services to replace the current in-process function calls. Define a protobuf service specification for the endorsement protocol including methods for processing EVM transactions, executing read-only calls, and querying state. Implement the gRPC server in the endorser to handle incoming proposal requests and the gRPC client in the gateway to send proposals and collect responses. Ensure proper error handling, timeout configuration, and connection pooling for production reliability. Update integration tests to validate the gRPC communication layer works correctly across network boundaries.

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**Quarter:** Q2

Start by locating the Gateway and Endorser entry points and tracing their current in-process function calls. Define the protobuf endorsement service for EVM transaction processing, read-only calls, and state queries, then implement both sides and update the integration tests. Done means requests work across network boundaries with error handling, timeouts, and connection pooling.

Written by the indexing model from the issue text.