Implement stub Windows IPC

[marceline-cramer]

Until we can get #175 fully fleshed out and implemented, let's just implement some stub IPC code that gets Hearth to compile on Windows even if IPC doesn't actually do anything at all.

We'll need to come up with a common interface for both UDS and named pipes (that preferably don't have any API differences between either) and make which implementation to use based on some #[cfg(...)] directive. hearth-daemon and hearth-ipc will both need to be updated, although maybe the daemon-side implementation should be moved into hearth-ipc too for simplicity's sake.