Original PR description

Problem:

Triggering the `child_of` operator in the testing framework caused an infinite loop that froze Odoo. This occurred because the framework attempted to fetch all children of the root operand without accounting for already visited nodes, resulting in children being added indefinitely.. Additionally, the original implementation had a O(n²) time complexity.

Solution:
Implemented a proper Depth-First Search (DFS) to retrieve all children and prevent duplicate traversal in O(n) time.