Use clock_gettime_nsec_np for current time

[koznobikhin]

Changed DispatchTime.now().rawValue to clock_gettime_nsec_np(CLOCK_MONOTONIC) to make it work correctly on Apple Silicon
Fixed subtraction test to make sense

[koznobikhin]

should fix the issue with the Spinner

[dominicegginton]

@koznobikhin
Many thanks for your time in contributing.

I have updated this branch to include running tests on both MacOS and Ubuntu GH runners and I see a currently failing test. I was unable to find a quick solution with the time I had the other weekend but will continue to look into this. Any help from the community here would be appreciated. Currently only able to easily locally test on my x86_64-linux based system, but the solution should be expected to work on aarch64-darwin, aarch64-linux, x86_64-darwin & x86_64-linux systems.

I would also like the keep this library compatible with Apple's MacOS, IOS, etc.... I wonder if clock_gettime_nsec_np falls under Apple's naughty list of kernel APIs due to its implementation calling mach_absolute_time directly, and would prevent this?