Expand `stc/Unix/Process.hpp` to Windows

[LunarWatcher]

stc/unix/Process.hpp currently doesn't support Windows, but it should.

Tasks:

1. Make sure everything Process.hpp supports can be done on Windows. If it can't, a discussion on what to do has to be had, as this may require revising the architecture of the class
2. Implement Windows support
3. Enable the tests for the class on Windows, and make sure they pass.
   • Some tests may need to be restricted on, or modified for Windows. This particularly applies to some of the tests running a shell
   • If bullet point 1 finds that some features aren't supported, some tests may need to be disabled on windows
4. Deprecate the final syscommand function; this change makes the Process API the canonical API for system commands