makevideo 0.3.0: built for speed

Built for speed. The same 74-second video, on the same CPU-only laptop, run back to back against v0.2.0:

	v0.2.0	v0.3.0
First render (no cached speech)	119.9 s	81.0 s
First render with --fast	n/a	36.3 s
Re-render (speech cached)	41.0 s	28.4 s

• --fast / "voice": "fast": a Piper voice that speaks at about 10× real time on 2 CPU threads. It sounds less natural than the default Kokoro voice, which suits drafts and long videos. The voices are joe (CC0) and norman (public domain).
• makevideo setup: pre-downloads the voice models once, so no render waits on a download.
• Render processes: scenes draw and encode in a process pool, so drawing is no longer limited to one thread.
• Tighter frame planning: each scene type knows its exact animation timing, which cuts the frames that need drawing by about 40%.
• Tuned speech: ONNX threads are pinned per process, and idle threads sleep instead of spinning.

Attached: the release video with the default voice, and the same video rendered with --fast (76 s of video in 30 s, cold) so you can compare the voices.