Cast single-band Raster to 2D

[rhugonnet]

Branched and re-merged into #351

This PR:

• Casts all single-band rasters from 3D to 2D when passed to the setter of Raster.data, or when used in an arithmetic operation that call Raster._overloading_check,
• Fixes some function behaviour and tests due to the previous point,
• Removes the option of having a list or tuple for Raster.nodata (as only int or float are used, anyway),
• Fixes some minor typing issues.