[sim] Change stepTiming to take seconds (#2599)

This is consistent with other WPILib timer functions.

wpilibc/src/main/native/cpp/simulation/SimHooks.cpp

@@ -28,7 +28,9 @@ void ResumeTiming() { HALSIM_ResumeTiming(); }
 
 bool IsTimingPaused() { return HALSIM_IsTimingPaused(); }
 
-void StepTiming(uint64_t delta) { HALSIM_StepTiming(delta); }
+void StepTiming(units::second_t delta) {
+  HALSIM_StepTiming(static_cast<uint64_t>(delta.to<double>() * 1e6));
+}
 
 }  // namespace sim
 }  // namespace frc