refactor: Split Numeric core extensions out.

These are not used directly by Time::Iterator, but are for convenience.
They may be removed later.

lib/time/iterator.rb

@@ -1,15 +1,8 @@
 require "active_support"
 require "active_support/core_ext/integer/time"
+require_relative "iterator/core_ext/numeric"
 require_relative "iterator/core_ext/time"
 
-# Inject 3.quarters
-class Numeric
-  def quarter
-    (3 * self).months
-  end
-  alias quarters quarter
-end
-
 class Time
   # Time iteration, and extra Time methods.
   module Iterator

lib/time/iterator/core_ext/numeric.rb

@@ -0,0 +1,7 @@
+# Inject 3.quarters
+class Numeric
+  def quarter
+    (3 * self).months
+  end
+  alias quarters quarter
+end

spec/time/core_ext/numeric_spec.rb

@@ -0,0 +1,13 @@
+RSpec.describe Numeric do
+  let(:time) { Time.now }
+
+  describe '#quarter(s)' do
+    [:quarter, :quarters].each do |method|
+      it 'adds 3 months per quarter' do
+        expect( time + 1.send(method) ).to eq time + 3.months
+        expect( time + 3.send(method) ).to eq time + 9.months
+        expect( time + 4.send(method) ).to eq time + 1.year
+      end
+    end
+  end
+end

spec/time/iterator_spec.rb

@@ -1,16 +1,6 @@
 RSpec.describe Time::Iterator do
   let(:time) { Time.now }
 
-  describe '#quarter(s)' do
-    [:quarter, :quarters].each do |method|
-      it 'adds 3 months per quarter' do
-        expect( time + 1.send(method) ).to eq time + 3.months
-        expect( time + 3.send(method) ).to eq time + 9.months
-        expect( time + 4.send(method) ).to eq time + 1.year
-      end
-    end
-  end
-
   describe '#iterate' do
     it 'uses an Enumerator' do
       expect( time.iterate(by: :day) ).to be_a(Enumerator)