fix(device): update assignment cache in autoAssignControllers and unassignAll

[hikaps]

Summary

• Fix m_assignmentCache not being updated in autoAssignControllers() and unassignAll(), causing auto-assigned controllers to lose their assignment on hotplug/reconnect during active sessions

Details

Both methods directly mutated m_devices but skipped updating m_assignmentCache, unlike assignDevice() which correctly maintains it.

autoAssignControllers() — two issues:

1. Initial unassign step cleared controller assignments from m_devices but left stale entries in the cache
2. Assign loop wrote assignments to m_devices but never wrote to the cache

unassignAll() — cleared all device assignments but never cleared the cache, so disconnected devices would incorrectly appear as "pending" for reconnection restoration.

The fix mirrors the existing assignDevice() pattern: remove cache entries on unassign, write qMakePair(instanceIndex, name) on assign.

Testing

• Build passes (100%)
• All 30 DeviceManager tests pass