Wait for gRPC server to fully shut down in Proxy destructor.

Adding `server_->Wait()` after `server_->Shutdown()` ensures that the gRPC server has completed its shutdown process and released all resources before the `Proxy` object is destroyed.

Ref: https://coroner.corp.google.com/#/crash/80b60a03-0000-2a67-96ae-14223bc4243e
PiperOrigin-RevId: 811447385
Change-Id: Ibb889f8f8db2e8bb1ae5e219c8a9e8101d00e742
1 file changed