Move to more flexible image containers for SilCam

[nepstad]

SilCam images are at present stored in NumPy binary files, and metadata (timestamp) is extracted from the file name itself. If we move to a more flexible container format we could have additional metadata stored with the images, and avoid the need for parsing file names and the restriction on file names this imposes.

Alternatives to investigate:

• NetCDF
• Zarr (https://zarr.dev/) - this is a cloud-friendly format as well, which could be useful going forward.