Fix browser crash: cap the whole-path walk length (constant-pace regression)

Paul hit a crash downloading MIDI from a large-coordinate loop URL (?m=787, path spanning y~16k-19k). Constant-pace made the loop length perim/speed

▶ Play it: Food Court Eternity → Smoke Arithmetic → Barometric Stampede — a constellation across three families — the path is the mix https://stellate.app/?genre=vaporwave&seed=8747&path=1679.4415,292.16891,1718.20526&xdur=0.046

bd3d6e4 https://github.com/aboard-io/stellate/commit/bd3d6e434e8f0dd895733b2117ed98073081778f