Fuzz slow I/O delay in ReconnectBench

[anthony-swirldslabs]

As suggested at #12315 (comment)

we want to fuzz the delay used in the slow I/O emulation in ReconnectBench to better emulate the real world behavior of hardware systems (disks and networks.) This would require us to re-implement the sleep() call to support microseconds-level sleep, and then use Random instances with parametrized seeds to fuzz the delay amount.