Extending unscope?

Hi there

I'm currently building an API with geared_pagination and was wondering if it would make sense to add `unscope(:select, :order, :group)` to [GearedPagination::Recordset#records_count](https://github.com/basecamp/geared_pagination/blob/96d51c1490d9c4754a74f7eada92e5ed76ee71af/lib/geared_pagination/recordset.rb#L32) as it otherwise causes some trouble with more complex queries. I don't think select, order and group are required here. But maybe I'm missing something?

For example here is a query that I'm trying to resolve:

```
Event.joins(:event_parts)
.where('event_parts.ends_at > ?', Time.zone.now)
.order(Arel.sql('min(event_parts.starts_at)'))
.group('events.id')
.preload(:event_parts)
```

Which results in an `TypeError: no implicit conversion of Integer into Hash` exception because the `count` result is grouped by `events.id`.

Start in lib/geared_pagination/recordset.rb at GearedPagination::Recordset#records_count and reproduce the Event.joins(:event_parts) query shown in the issue. Inspect how the grouped relation is counted and evaluate the proposed unscope of select, order, and group. Done means the example no longer raises TypeError and the count behavior remains correct for ordinary relations.

Written by the indexing model from the issue text.