PHLEGM v9 r65 — Commodore MOS-6502 accelerated display scheduling

Observed issue (r64): MOS-6502 PET/CBM FPS declines at approximately SPEED 270% and higher. r64 sends every emulated character-display refresh to the host renderer for numerical speeds, while only UNLIMITED coalesces host paints. At 270% a nominal 50/60 Hz display requests approximately 135/162 paints per wall second. Such work shares the CPU execution thread; driver/paint overhead can dominate higher-speed runs. There is no special 270% CPU limiter in cycles.bi.

Source changes:
- Numeric SPEED above 100% now shares the existing Unlimited presentation cap for character-ROM displays; <=100% and numeric native-raster paths retain the old behavior.
- Clock domains, MOS-6502 instructions, VIA/PIA clocks, audio timing, retrace, and emulated video edges remain in emulated machine time. GPU presentation skips may discard an intermediate image; they do not skip the emulated refresh event.
- A separate, unsaved character-screen refresh counter counts *all* scheduled emulated edges (including intermediate coalesced frames) for FPS. FrameSkipPending tracks unpresented edges. The display's serialized frameNumber retains its existing meaning for macros/sessions and native-raster paths.
- No new mandatory ROMs, compiler/runtime dependencies or file-format changes.

Important validation limitation: Source-level contracts and a deterministic reference scheduler test verify changes and exercise the cap at 100%, 200%, 270%, 400%, 1000%, and Unlimited, but cannot measure your actual host GPU/SDL throughput. On Windows, run the same PET/CBM model and program with SPEED 100, 200, 270, 400, 1000, UNLIMITED. Compare both FPS and RT with the r64 baseline. Testing SOUND ON/OFF and with/without the display visible can separate any remaining audio or GPU stalls.

If FPS remains lower at higher SPEED while RT does not, the original issue may also involve frame-meter semantics; if both decline despite the host cap, gather per-subsystem timing from the host before changing core MOS-6502 or support-chip clocking.
