implement decrby (for desting from CI)

Author: mgravell

toys/StackExchange.Redis.Server/RedisServer.cs

@@ -1132,6 +1132,10 @@ protected virtual TypedRedisValue Incr(RedisClient client, in RedisRequest reque
         protected virtual TypedRedisValue Decr(RedisClient client, in RedisRequest request)
             => TypedRedisValue.Integer(IncrBy(client.Database, request.GetKey(1), -1));
 
+        [RedisCommand(3)]
+        protected virtual TypedRedisValue DecrBy(RedisClient client, in RedisRequest request)
+            => TypedRedisValue.Integer(IncrBy(client.Database, request.GetKey(1), -request.GetInt64(2)));
+
         [RedisCommand(3)]
         protected virtual TypedRedisValue IncrBy(RedisClient client, in RedisRequest request)
             => TypedRedisValue.Integer(IncrBy(client.Database, request.GetKey(1), request.GetInt64(2)));