PHLEGM v6 - Unlimited emulation / frame-skip diagnostic patch

- Unlimited emulation no longer requires host rasterization/presentation for every emulated video refresh.
- Emulated video/PPU timing continues normally; intermediate host frames are coalesced when emulation outruns wall time.
- Normal paced emulation retains the existing per-refresh presentation behavior.
- The lower-left diagnostic overlay now shows frame skip immediately to the right of FPS as: FPS xxx.xx  FS xxx
- FS is measured from actual emulated refreshes omitted from host presentation, not a configured/cosmetic value.
