Implement Process::Status.wait

[eregon]

Requested by @ioquatix, to fix https://github.com/socketry/event/pull/6/checks?check_run_id=2807838780

This is a new Ruby 3 method, it's the same as Process.wait but without setting $?, so it should be fairly straightforward to add.

There are no specs currently, we should add some basic specs for it.

[bjfish]

This has been implemented at 2b88831.

[ioquatix]

Thanks!!!