Add rounding option in multiresolution scaling factor deduction

[kgabor]

The zarr metadata contains floating point scaling in real world coordinates while the bdv data model scales compared to the finest resolution image. These numbers should come back as the 2x downscaling factors, however we have floating-point inaccuracies. Add rounding option e.g. to 3 or 4 digits to round to get back the nominal factors properly.