DiskDevice: work with LBA devices

Discovered in Calamares [0] with specific device size 24GiB, the rounding from LBA total sectors to CHS loses precision in calls to the constructor and results in totalSectors() returning an inaccurate value.

I've been exploring a minimally invasive way to support LBA alongside CHS. This is a first draft idea (not yet compiled or tested) to get feedback.