Settle.upTo constructor

Pump while the app keeps asking for frames, stopping at the first frame it does not — or when budget of the fake clock is spent, whichever comes first. Running out is not a failure — it is recorded on the step — unless strict, which makes it one after the step's real work has been landed. See Settle.strict.

The budget is a ceiling, not a wait. Frames are the only thing this loop follows, and work waiting on a timer schedules none: a screen whose Future.delayed(Duration(seconds: 1)) has not completed looks exactly like a screen that is finished, so the loop returns at the first quiet frame — 100ms in — with the second still on the clock, and the tree is disposed under it. That is pumpAndSettle's contract too, and a caller that means to wait for a timer has to say so: Settle.elapse, or a Settle.frames count that covers it.