Fix process group behavior on Windows

[filiptibell]

This PR fixes the process group behavior on Windows and makes sure descendant processes are properly reaped together with the main Rokit runner process job that spawned them. This unfortunately broke due presumably to some internal mechanisms in command-group and therefore its successor crate process-wrap changing.

• Version 1 of command-group works as expected (this is what Foreman and Aftman use)
• Version 2+ of command-group did not initially work as expected - but now works the same as v1 after migrating to the .group() builder API
• Unfortunately, no versions of process-wrap have worked out so far. Their examples of migrating from different versions of the command-group crate do not preserve the same behavior that the older crate had.