Add support for macOS

[kalbasit]

This PR adds support for macOS through the pmset command.

The PR is currently draft as I need more time to document the UDP part in the README, but would appreciate an early review on what I've got so far.

[SR-G]

Hello.

Thanks for the PR. I'll integrate it once final.

Regarding the macOS support, i would expect indeed only the "sleeper_darwin.go" to be added.
About the README.md, maybe there are some manipulations to be done at OS level, like for linux, in order for the binary to receive the UDP packets (and maybe this is what you are speaking about here), but other than that, i would not expect any change in the listener_udp.go class.

About the sleeper_darwin.go it seems quite straightforward / similar to the sleeper_linux.go, so should be fine at first glance.

[kalbasit]

Thank you for the pre-review, I appreciate it. Yes that's what I'm talking about, I need to ensure that UDP works and I need time to test that. My apologies for the delay I've been pretty busy, hopefully I'll get to it by the end of this week and will update the PR and remove draft status when I'm satisfied that it's ready for your final review.