ActiveRecord `count` with a Relation#group returns a hash, not an integer, which break Pagination

I came across this bug in a large Rails API my team is building. The issue is that ActiveRecord count method does not always return an integer. As explained in the docs:

If count is used with Relation#group, it returns a Hash whose keys represent the aggregated column, and the values are the respective amounts:

Person.group(:city).count
# => { 'Rome' => 5, 'Paris' => 3 }

This breaks the expectation made in the various Paginator classes that record_count will be an integer.

The simple way to fix this is to handle the Hash case with hash.values.sum. I am putting in this Issue, instead of a MR, because I am not certain where in the stack you would think this should live. It could live in the AR adapter for find_count, it could live in the Processor when page_options[:record_count] is created, or it could live in the Paginator class.

If you give me any guidance on how you would like to fix this bug, I will happily put in the appropriate MR.

stephen