Exempt pipelined clients from SHM frame pacing (fixes Mewgenics stutters) (#1862)

A client that streams SHM blits without a per-frame sync (Mewgenics
cutscenes) only feels read-suspension back-pressure in whole batches,
so any pacing granularity chops its loop into freeze and catch-up
bursts. Detect the pattern - repeated pause supersedes within one pause
window, which per-frame-syncing clients never produce - and run such
clients uncapped instead.

Co-authored-by: Utkarsh Dalal <utkarsh.dalal@toptal.com>