[Bug] Proxy remoting CHECK_CLIENT_CONFIG always returns success

### What happened?

The Proxy remoting implementation of `RequestCode.CHECK_CLIENT_CONFIG` currently creates a success response without validating the request body.

Broker-side handling validates `CheckClientRequestBody`, including filter expression type support and expression parse errors, and returns an error response when the client config is invalid. The Proxy remoting path should preserve that behavior instead of always returning success.

### Expected behavior

Proxy remoting `CHECK_CLIENT_CONFIG` should decode and validate the request in the same way as the broker path, returning an error response for unsupported or invalid subscription expressions.

### Scope

RocketMQ Proxy / remoting compatibility. This is related to the Proxy Admin and client diagnostics track because invalid client subscription configuration should be visible through the Proxy path.

### Suggested fix

Decode `CheckClientRequestBody`, validate expression type and expression syntax, and return the corresponding remoting error code when validation fails.

Trace the Proxy remoting handler for RequestCode.CHECK_CLIENT_CONFIG and compare it with the broker-side handling of CheckClientRequestBody. Check how expression type support, parse errors, and remoting error codes are handled; done means invalid subscription expressions produce an error response through Proxy remoting instead of success.

Written by the indexing model from the issue text.