Extend NumericalityValidator to check precision and scale

Use new checks on Unit.multiplier
Closes #28

config/initializers/core_ext.rb

@@ -1,5 +1,9 @@
 require 'core_ext/big_decimal_scientific_notation'
 
+ActiveSupport.on_load :active_record do
+  ActiveModel::Validations::NumericalityValidator.prepend CoreExt::ActiveModel::Validations::NumericalityValidatesPrecisionAndScale
+end
+
 ActiveSupport.on_load :action_dispatch_system_test_case do
   prepend CoreExt::ActionDispatch::SystemTesting::TestHelpers::ScreenshotHelperUniqueId
 end

config/locales/en.yml

@@ -1,4 +1,8 @@
 en:
+  errors:
+    messages:
+      precision_exceeded: must not exceed %{value} significant digits
+      scale_exceeded: must not exceed %{value} decimal digits
   activerecord:
     attributes:
       unit: