Avoid logging full gRPC responses in proxy ResponseWriter

## Problem

`ResponseWriter` logs the full gRPC response object before writing and again when the client has cancelled the request. Some proxy responses, especially receive-message responses, can carry message payload data. Logging the full protobuf response can therefore expose message bodies or other request data in proxy logs.

## Scope

Track 2 / Proxy Admin and gRPC diagnostics hardening. This is a logging-safety change only; it should preserve response write behavior.

## Expected behavior

- Do not log full gRPC response protobuf contents in `ResponseWriter`.
- Keep useful diagnostics such as response type and status/code when available.
- Add targeted tests to ensure receive-message payload bytes are not present in log summaries.

## Evidence

- `proxy/src/main/java/org/apache/rocketmq/proxy/grpc/v2/common/ResponseWriter.java` logs `response` directly in debug/warn paths.
- `ResponseWriter` is used by `ReceiveMessageResponseStreamWriter`, so receive responses can pass through this common logging path.

Start with proxy/src/main/java/org/apache/rocketmq/proxy/grpc/v2/common/ResponseWriter.java and trace how ReceiveMessageResponseStreamWriter uses it. Review the debug and warning paths, then add targeted tests showing that receive-message payload bytes are absent while response type and status/code diagnostics remain available. Done means response writing is unchanged and full protobuf contents are no longer logged.

Written by the indexing model from the issue text.