wayland: optimize frame scheduling for 120Hz+ displays

[Gong-Mi]

Problem

On Cinnamon Wayland with high refresh rate displays (120Hz+), window flickering occurs due to tight frame scheduling:

• +EBUSY+` waits a full refresh cycle before retrying, adding exactly one frame of latency on any scheduling hiccup.

Environment

• GPU: AMD Radeon 880M (RDNA 3.5, amdgpu driver)
• Display: 2560×1600 @ 120Hz (BOE eDP-1)
• Session: Cinnamon 6.6.7 Wayland
• Kernel: Linux with DRM atomic

Changes

1. Wayland: remove fixed 2ms sync delay

File: +src/compositor/compositor.c+`

On Wayland the KMS page-flip event already provides synchronization. The 2ms delay is a legacy X11 artifact (for +GL_EXT_x11_sync_object+`) that hurts high-refresh-rate performance. X11 path is kept unchanged for compatibility.

2. Faster page-flip retry on EBUSY

File: +EBUSY+` without stalling a full frame.

Testing

1. Disable experimental feature to eliminate offscreen overhead:
   ++`

2. Apply patch and rebuild muffin.

3. Observe flickering significantly reduced or eliminated on 120Hz panel.

Related gaps (not addressed in this PR)

• +wp_tearing_control_manager_v1+` Wayland protocols are not yet implemented in Muffin. Adding these would allow clients to better synchronize with the compositor and optionally allow tearing for latency-critical content.