[Bug] Proxy client settings cleaner logs full gRPC Settings

## Problem

`GrpcClientSettingsManager` logs full gRPC `Settings` protobufs from the periodic unused-settings cleanup path.

Evidence:
- `proxy/src/main/java/org/apache/rocketmq/proxy/grpc/v2/common/GrpcClientSettingsManager.java` logs `settings:{}` when removing unused gRPC client settings.

## Impact

This is in the RocketMQ Studio Track 2 / Proxy Admin diagnostics scope. Full Settings can include detailed publish/subscription metadata. Cleaner logs should not dump those payloads.

## Expected

The cleaner log should use a compact summary such as client type and publish/subscription counts instead of full protobuf output.

Start with proxy/src/main/java/org/apache/rocketmq/proxy/grpc/v2/common/GrpcClientSettingsManager.java and inspect the periodic unused-settings cleanup path that logs the gRPC Settings protobuf. Replace the full Settings output with a compact summary containing the client type and publish/subscription counts. Done means cleaner logs no longer dump detailed Settings payloads.

Written by the indexing model from the issue text.