Use #size instead of #count for pagination

`#count` will always execute an SQL COUNT query whereas `#size` will
check if the records are already loaded (and then call `#length`). It
only executes a count when necessary.

See https://api.rubyonrails.org/classes/ActiveRecord/Relation.html#method-i-size

Author: coffeejunk

lib/jsonapi/pagination.rb

@@ -63,7 +63,7 @@ def jsonapi_pagination_meta(resources)
       numbers = { current: page }
 
       if resources.respond_to?(:unscope)
-        total = resources.unscope(:limit, :offset, :order).count()
+        total = resources.unscope(:limit, :offset, :order).size
       else
         # Try to fetch the cached size first
         total = resources.instance_variable_get(:@original_size)