Add helper to format an academic year

This adds a helper method which formats an academic year as a range of
two years as per the design.

Author: thomasleese

app/helpers/academic_years_helper.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+module AcademicYearsHelper
+  def format_academic_year(academic_year)
+    "#{academic_year} to #{academic_year + 1}"
+  end
+end

spec/helpers/academic_years_helper_spec.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+describe AcademicYearsHelper do
+  describe "#format_academic_year" do
+    subject { format_academic_year(2025) }
+
+    it { should eq("2025 to 2026") }
+  end
+end