lxd/cgroup: Implement proper typing
lxd/cgroup: Implement proper typing

This changes the various functions to deal with int64 rather than
obscure strings in many cases. Also renames a few functions to have more
meaningful names and improves handling of -1/max for cgroup2

As part of this, memsw functions perform the needed math directly
instead of relying on the caller doing it.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

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