Display mode at 120 Hz previously waited two display-link ticks per frame
and stayed at 60 fps. Count its acquire waits in the link's own ticks so
120 fps takes one tick. Carry fractional ticks across frames so requests
such as 90 fps on a 120 Hz link wait four ticks per three frames.
Keep game-interval and frame-step pacing in 60 Hz vsync units. Extend
t_link_ticks through the production acquire path, add it to CPU-only CI,
and document the behavior in the frame-rate reference and symptom index.
Validation: 20 link-tick checks, 154 NVN integration checks, pacing and
frame-step tests, Metal snapshot and display-link rescue tests, Mac host
build, iOS source compilation, and documentation checks passed. Physical
display gameplay and iPhone gameplay were not retested.
Co-authored-by: v0lumehi <aljic.zijad@gmail.com>
