Add a simple benchmark

.readygo

@@ -0,0 +1 @@
+{"readygo_file_format_version":1,"benchmark_results":[["message serialization decoding",[0.00777734375,0.007609375,0.00721875,0.00836328125,0.007546875,0.0088046875,0.0069414062500000005,0.007550781249999999,0.0072734374999999995,0.009625,0.007867187500000001,0.01226953125,0.0073984375,0.007292968750000001,0.00937890625,0.0073750000000000005]]]}

benchmarks/message_encoding.rb

@@ -0,0 +1,21 @@
+require "kafka"
+
+ready "message serialization" do
+  before do
+    message = Kafka::Protocol::Message.new(
+      value: "hello",
+      key: "world",
+    )
+
+    @io = StringIO.new
+    encoder = Kafka::Protocol::Encoder.new(@io)
+    message.encode(encoder)
+
+    @decoder = Kafka::Protocol::Decoder.new(@io)
+  end
+
+  go "decoding" do
+    @io.rewind
+    Kafka::Protocol::Message.decode(@decoder)
+  end
+end