Clean up the entireCommands child process group by default #5303

Commands that spawn child processes can sometimes leave sub-sub-processes lingering if the invoked Command does not reap them on its own.

Counterintuitively, I think we should be leveraging the detached: true flag by default to address this. This would be in-line with the scoped managed resource approach that Effect is already taking with Command execution today. Whether we should offer an escape hatch for this default or not I don't have an opinion on.

First of all, note that detached: true behavior differs by platform. More about that here: https://nodejs.org/api/child_process.html#child_process_options_detached

I'm proposing that we set detached: true by default for non-windows systems.

detached: process.platform !== "win32"

This will cause the new process to be assigned as a leader of a new process group that can then be terminated in its entirety at our discretion.

Instead of just forwarding a kill signal to the process handle (handle.kill(signal)), we'd then utilise taskkill with /T on windows (kill the entire process tree) and process.kill(-pid, signal) (negative pid to kill the entire process group) on non-windows systems.

References:

https://nodejs.org/api/child_process.html#child_process_options_detached
https://github.com/Kikobeats/kill-process-group/blob/master/src/index.js