Save split channel TIFFs using the metadata from Cockpits new mosaic DV files

Recent changes in Cockpit that adds more metadata to the mosaic images https://github.com/microscope-cockpit/cockpit/commit/df8f1f09ff59c20248d2e538be25be9607068768, which can be used to split the channels. [PySIMRecon's get_image_data function](https://github.com/DiamondLightSource/PySIMRecon/blob/main/src/sim_recon/images/dv.py#L202) is a good start. From there, writing multi-channel OME-TIFFs should be fairly straight forward.

This would also mean the current fluorescence filtering methods should be removed. If a brightfield-only image is wanted, the fluorescence channels can simply be thrown away. There probably should be a new argument (both CLI and functions) for this option.

The DV files have been made compatible (i.e. aren't rejected) since #9.