Meta: Improve portability with compat for non-GNU, non-sudo systems

[sdomi]

This MR fixes the build scripts on Alpine w/o coreutils (and other distros without GNU and sudo :p)

Firstly, we depend on GNU-specific du switch --apparent-size. Busybox has this implemented, but as -b instead.

Secondly, there's now logic to detect if your system has doas instead of sudo. If the user has neither, we bail out quickly instead.

[BuggieBot]

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[sdomi]

Improving and unifying the remaining dependency checks is something I may tackle on a later rainy day :p