The Gen2 obs_subaru policy file policy/HscMapper.yaml defines bias and dark calibrations to be of type ImageF, which, by definition, does not have mask or variance planes. On read, these are passed through a standardization step that converts ImageF to an ExposureF by adding empty mask and variance planes. However, when running a comparison test using Gen3 middleware (on DM-28936), it was revealed that these files do have variance and masks planes, it turns out these calibration files do have mask and variance planes and uses them when updating the variance planes throughout the processing. So, as it stands, Gen2 and Gen3 are behaving slightly differently leading to small (and very likely scientifically insignificant) differences, putting a dent in our efforts towards acheiving Gen2/Gen3 parity through Single Frame Processing. The fix is to update the bias and dark formats in the policy file from ImageF to MaskedImageF, which will be done here.