Description:
When assigning a specific copper layer to a net class under the Net Classes settings, freerouting seems to ignore this setting. Tracks are still routed on other layers, even though the net class is explicitly restricted to a single layer.

Steps to Reproduce:

1. Open a design in freerouting.
2. Go to Net Classes and create or edit a net class.
3. In the layer assignment section, select only one copper layer (e.g., bottom).
4. Assign this net class to one or more nets.
5. Start the autorouter.

Expected Behavior:
The autorouter should only place tracks for that net class on the assigned copper layer.

Actual Behavior:
Tracks are routed on layers that are not assigned in the net class, ignoring the restriction.

System Information:
freerouting version: Latest (as of June 2025)
Operating System: Windows

Additional Notes:
This issue makes it impossible to enforce routing constraints for specific nets, which is important for high-frequency or power-specific traces.