feat: add Measured::Temperature unit type

Add Temperature as an opt-in unit type with Celsius, Kelvin, and
Fahrenheit. Not included in the default require - users opt in with:

  gem 'measured', require: ['measured', 'measured/temperature']

Or manually: require 'measured/temperature'

Author: ntn

lib/measured/temperature.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+require "measured/base"
+require "measured/units/temperature"

lib/measured/units/temperature.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+Measured::Temperature = Measured.build do
+  unit :C, aliases: [:celsius]
+
+  unit :K, aliases: [:kelvin], convert_to: "C",
+    forward: ->(k) { k - BigDecimal("273.15") },
+    backward: ->(c) { c + BigDecimal("273.15") },
+    description: "celsius + 273.15"
+
+  unit :F, aliases: [:fahrenheit], convert_to: "C",
+    forward: ->(f) { (f - 32) * Rational(5, 9) },
+    backward: ->(c) { c * Rational(9, 5) + 32 },
+    description: "celsius * 9/5 + 32"
+end

test/units/temperature_test.rb

@@ -1,20 +1,7 @@
 # frozen_string_literal: true
 
 require "test_helper"
-
-Measured::Temperature = Measured.build do
-  unit :C, aliases: [:c, :celsius]
-
-  unit :K, aliases: [:k, :kelvin], convert_to: "C",
-    forward: ->(k) { k - BigDecimal("273.15") },
-    backward: ->(c) { c + BigDecimal("273.15") },
-    description: "celsius + 273.15"
-
-  unit :F, aliases: [:f, :fahrenheit], convert_to: "C",
-    forward: ->(f) { (f - 32) * Rational(5, 9) },
-    backward: ->(c) { c * Rational(9, 5) + 32 },
-    description: "celsius * 9/5 + 32"
-end
+require "measured/units/temperature"
 
 class Measured::TemperatureTest < ActiveSupport::TestCase
   test ".unit_names should be the list of base unit names" do
@@ -84,7 +71,7 @@ class Measured::TemperatureTest < ActiveSupport::TestCase
   end
 
   test ".unit_names_with_aliases includes all aliases" do
-    expected = %w(C F K c celsius f fahrenheit k kelvin).sort
+    expected = %w(C F K celsius fahrenheit kelvin).sort
     assert_equal expected, Measured::Temperature.unit_names_with_aliases
   end