Proposal: kqueue support based on polling crate

[xanderio]

I'm currently looking into adding support for kqueue to support BSD platforms.

After a bit of digging i found the polling crate from the smol-rs team.
The crate it self lists macOS, iOS, FreeBSD, NetBSD, OpenBSD, and DragonFly BSD as supported platforms for kqueue.

Would PR adding polling based KqueueWatcher be accepted?

[0xpr03]

Yep, see #273 (and also here for all the kqueue mentions about better support through that ;) )

[0xpr03]

A bit of warning though: The current structure/implementation for the other systems is a little bit blurry as some stuff got changed/removed without a real new replacement. See for example here. It's totally fine if you just copy the feature parity of the inotify implementation (for which I can speak) and not implement for example the precise config optionality. Still I'd welcome some hints in the code for unsafe for why it's safe and also where you'd have to flip something to reach/implement unprecise* events.

* With unprecise I mean the PreciseEvents option we want to reach.