add support for luksSuspend/luksResume

[Narrat]

May come in handy for hibernation/suspending the OS without completly closing the tomb.

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Just a POC for #34 without a full close operation, but still avoiding writing the secret to places where it shouldn't be. Not fully fleshed out, as bind mounts are ignored, operations on a suspened device are allowed. But it is imo enough to play around with and decide if it is worth or close (or slam) is enough.