Support TT_VISIBLE_DEVICES for Mock Cluster as well

Implement TT_VISIBLE_DEVICES support for Mock Cluster as well. This should go in after #2057. It should support @Riddy21's case of taking both local and remote chips for Mock Clusters, basically match the flow of TT_VISIBLE_DEVICES in silicon.

<img width="1468" height="1016" alt="Image" src="https://github.com/user-attachments/assets/4ec08aff-0d21-4716-89f6-f65308552b1d" />