feat: block running commands / proxying when system is being deleted

Large systems take way too long to delete, which causes any insert for that system to block a connection, which exhausts the connection pool

Myriad/Rest/Types/Requests/MessageRequest.cs

@@ -10,4 +10,6 @@ public record MessageRequest
     public AllowedMentions? AllowedMentions { get; set; }
     public Embed[]? Embeds { get; set; }
     public MessageComponent[]? Components { get; set; }
+    public Message.Reference? MessageReference { get; set; }
+
 }