[12.x] Allow touch() to accept multiple columns

[devajmeireles]

This PR extends Builder::touch() and Model::touch() to accept an array of column names, allowing multiple timestamp columns to be updated in a single query.

Before

$model->touch('published_at');

$model->touch('verified_at'); // two queries

After

$model->touch(['published_at', 'verified_at']); // single query

Both touch() and touchQuietly() on the model, as well as Builder::touch(), now accept string|array|null. Full backward compatibility was preserved, ensuring that introducing this feature will not break anything.