Migrate `/v1/_x2m/block/notarized_block/get` to grpc

This issue has no description.

The issue mentions migrating a specific HTTP endpoint to gRPC. First, locate the existing `/v1/_x2m/block/notarized_block/get` route in the codebase, likely in an HTTP handler or router. Then, understand the current request/response format. Research the project's gRPC setup and protobuf definitions to see how other endpoints are structured. Implement the new gRPC service method and update any client calls. Testing involves verifying the new gRPC endpoint returns the same data as the old HTTP endpoint.

Written by the indexing model from the issue text.