refactor: centralize protobuf and remove go-zero

shared/grpcconn/provider.go

@@ -0,0 +1,9 @@
+// Package grpcconn defines the smallest connection contract required by generated RPC clients.
+package grpcconn
+
+import "google.golang.org/grpc"
+
+// Provider is implemented by grpc.ClientConn wrappers, including legacy clients exposing Conn.
+type Provider interface {
+	Conn() *grpc.ClientConn
+}