Now that `LiveRuntimeWorker` does all the blocking IPC off the UI
thread, the 16 ms shell tick is no longer the bottleneck — drop it to
8 ms (≈ 125 Hz) so a 120 Hz display can present a fresh Servo frame
between every refresh. The worker queue still coalesces, so doubling
the rate does not double the wire traffic.
Replace `fade_in`'s linear ramp with an ease-out cubic so panel /
overlay reveals decelerate the way the design tokens promise instead
of cutting in abruptly at the end. Unit-tests pin the curve shape so a
future refactor that wires in a different easing function won't
silently revert to linear.
ZacharyZhang-NY
5548427df3