Method GroupByRedb<TKey>(Expression<Func<IRedbObject, TKey>>)

Grouping by base IRedbObject fields (id, scheme_id, parent_id, etc.)
Uses IRedbObject for compile-time safety - Props not visible!
Pro version receives FilterExpression directly for proper SQL compilation.

public virtual IRedbGroupedQueryable<TKey, TProps> GroupByRedb<TKey>(Expression<Func<IRedbObject, TKey>> keySelector)