be more CPU-efficient, particularly when not running

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When running, it seems like burning 10% CPU or so, even on a high end system, to keep the animation running with reasonable fluidity is just non-negotiable (Facilitimer, which displays a similar progress progress bar, uses similar CPU).

But when the bar is not displayed, we can know in advance what the next interesting inflection point in our schedule is, and just fully go to sleep and not schedule anything until that point.

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I'm pretty happy with the "pulse the progress bar periodically" solution to this, which (A) draws the eye only intermittently, which is better than constant slow motion which keeps attention focused on it, and (B) addresses the effective "CPU leak" of having it running.