Add option for executing queries with load_async

[aesnyder]

I am speeding up some of our controllers and noticed that I cannot use load_async with pagy.

I have it roughly working by overriding the method as such:

OLD

    def pagy_countless_get_items(collection, pagy)
      return collection.offset(pagy.offset).limit(pagy.limit) if pagy.vars[:countless_minimal]

      fetched = collection.offset(pagy.offset).limit(pagy.limit + 1).to_a # eager load limit + 1
      pagy.finalize(fetched.size)                                         # finalize the pagy object
      fetched[0, pagy.limit]                                              # ignore eventual extra item
    end

NEW

def pagy_countless_get_items(collection, pagy)
    if pagy.vars[:countless_minimal]
      query = collection.offset(pagy.offset).limit(pagy.limit)
      if pagy.vars[:load_async]
        return query.load_async
      end
      query
    else
      query = collection.offset(pagy.offset).limit(pagy.limit + 1)
      if pagy.vars[:load_async]
        query = query.load_async
      end
      fetched = query.to_a                                                   # eager load limit + 1
      pagy.finalize(fetched.size)                                         # finalize the pagy object
      fetched[0, pagy.limit]                                              # ignore eventual extra item
    end
  end

My plan would be to add this to both countless and the regular pagy method.

[ddnexus]

Nice article about a similar topic: https://www.rorvswild.com/blog/2025/optimize-pagination-speed-with-asynchronous-queries-in-ruby-on-rails