Avoid allocations when using delay_serialization (#295)

Co-authored-by: ywenc <[email protected]>

lib/datadog/statsd.rb

@@ -431,7 +431,7 @@ def send_stats(stat, delta, type, opts = EMPTY_OPTIONS)
       if sample_rate == 1 || opts[:pre_sampled] || rand <= sample_rate
         full_stat =
           if @delay_serialization
-            [[stat, delta, type], {tags: opts[:tags], sample_rate: sample_rate}]
+            [stat, delta, type, opts[:tags], sample_rate]
           else
             serializer.to_stat(stat, delta, type, tags: opts[:tags], sample_rate: sample_rate)
           end

lib/datadog/statsd/message_buffer.rb

@@ -28,7 +28,8 @@ def add(message)
         # Serializes the message if it hasn't been already. Part of the
         # delay_serialization feature.
         if message.is_a?(Array)
-          message = @serializer.to_stat(*message[0], **message[1])
+          stat, delta, type, tags, sample_rate = message
+          message = @serializer.to_stat(stat, delta, type, tags: tags, sample_rate: sample_rate)
         end
 
         message_size = message.bytesize

spec/integrations/delay_serialization_spec.rb

@@ -6,7 +6,7 @@
     # expects an Array is passed and not a String
     expect(buffer)
       .to receive(:add)
-      .with([["boo", 1, "c"], {tags: nil, sample_rate: 1}])
+      .with(["boo", 1, "c", nil, 1])
     # and then expect no more adds!
     expect(buffer).to receive(:add).exactly(0).times
     expect(buffer)