OptionalidExplicit sweep id. Normally generated from nowMs; pass this to make a
sweep's ids fully deterministic (tests) or to resume a known id.
OptionallaunchMin ms between launches. Passed to FanOut.
OptionalmaxMax instances running at once (0 = all at once). Passed to FanOut.
OptionalnameSweep name; also the launched instances' name prefix. Default "sweep".
OptionalnowTime (ms epoch) used to stamp a generated sweep id. Required if id unset.
Options for building/launching a sweep.