add count method support

[jmbarberan]

vscode intelliphense show error for count method not found for example:

$subscription_type = 'VIP'; $rows = Account::find([ 'conditions' => 'subscription_type = :type:', 'bind' => [ 'type' => $subscription_type ] ]); $items_count = $rows->count(); // count() calling showing error

[Jeckerson]

This implementation is redundant, as it extends from Resultset abstract class

https://github.com/phalcon/ide-stubs/blob/80709ecaf79f86ec3dbd9c059aa4fda2fed5e7c6/src/Mvc/Model/Resultset.php#L146