/// Delta time in integer milliseconds — avoids floating point in
/// animation hot paths on targets without an FPU.
;
/// Global monotonic clock resource. Single time source for the entire
/// App — animation, gesture recognition, simulated input, render
/// timing all read from this.
///
/// `clock` is a fn pointer returning nanoseconds since an arbitrary
/// epoch (typically app init). Plugins set it: `StdInstantClockPlugin`
/// on desktop, `SystimerClockPlugin` on ESP.