put in class stub as per profiling

Author: p

lib/datadog/core/ddsketch.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Datadog
+  module Core
+    # This class exists to wrap a ddsketch_Handle_DDSketch into a Ruby object.
+    #
+    # This class is not empty; all of this class is implemented as native code.
+    class DDSKetch # rubocop:disable Lint/EmptyClass
+    end
+  end
+end