Summary

This PR adds native DisplayLink brightness and contrast control for displays managed by DisplayLink Manager.

Changes:

• Adds a DisplayLink notification wrapper for display discovery, brightness writes, and contrast writes.
• Maps DisplayLink displays to MonitorControl displays through the DisplayLink-provided CGID.
• Uses DisplayLink native brightness instead of software shade control when DisplayLink control is available.
• Adds DisplayLink contrast support to the existing contrast slider and keyboard paths.
• Mirrors brightness and contrast changes made in DisplayLink Manager back into MonitorControl state and active menu sliders.
• Coalesces DisplayLink slider writes on a background queue to avoid request bursts during fast dragging.
• Keeps the existing software brightness fallback when DisplayLink control is unavailable before queueing a brightness write.

Tested

• DisplayLink Manager version: 16.1.
• Real-machine test passed on macOS 26.5 (25F71).
• DisplayLink brightness adjustment works.
• DisplayLink contrast adjustment works.
• External brightness and contrast changes made in DisplayLink Manager are reflected back in MonitorControl.