Add grpc-status trailers to fake gRPC responses

[yuandrew]

What was changed

updated the two fake-success response builders to stream a final trailer frame containing grpc-status: 0

Why?

tonic version bumped, grpc/grpc-rust#2543

Our fake gRPC success responses are malformed, they send HTTP 200 plus a framed protobuf body, but they do not send the required final grpc-status: 0 trailer. Newer tonic correctly treats that as an invalid/truncated gRPC response, so tests fail with missing grpc-status trailer.

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

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Note

Low Risk
Low risk: changes only how synthetic success responses are constructed by adding a standard gRPC trailer, with minimal impact beyond test/fake transports.

Overview
Updates the callback-based gRPC service and integration-test fake server helpers to stream a final trailers frame containing grpc-status: 0 after successful response data.

This replaces previous “data-only” success bodies with StreamBody/Frame-based bodies so responses are well-formed under newer tonic validation.

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