chore(growth): apply scorer behaviour in indicators

lib/growth/score/head_circumference.ex

@@ -2,4 +2,17 @@ defmodule Growth.Score.HeadCircumference do
   @moduledoc """
   Calculate z-score for head circumference for age.
   """
+
+  @behaviour Growth.Score.Scorer
+
+  alias Growth.Score.Scorer
+
+  @impl Scorer
+  @spec measure_name() :: atom()
+  @doc """
+  Name of the measurement used in head circumference indicator.
+  """
+  def measure_name do
+    :head_circumference
+  end
 end