Update ToO infrastructure to handle larger target files

[geordie666]

The ToO program was approved for a larger number of secondary targets. The current ToO-fiber.ecsv file is getting too large to be comfortably handled by fiberassign-on-the-fly, though.

Refactor the ToO-fiber.ecsv file to instead comprise multiple files by year, or even month, e.g. ToO-fiber-2025.ecsv, so that the files are smaller and easier for fiberassign to digest.

[sybenzvi]

@geordie666, we should be careful about annual and/or monthly boundaries. This may be the edgiest of edge cases, but I could imagine a situation where we prep a ToO list for processing, and then something (like a perlmutter outage) interrupts their incorporation into the MTL. If the month rolls over before we can update the target list again, a batch of ToOs could be ignored.

What if instead, we keep writing to the same ToO-fiber.ecsv, but part of the processing automatically moves expired ToOs into a backup file (ToO-fiber-expired.ecsv) as the date shifts beyond their observing window? Then ToO-fiber.ecsv stays relatively small, and we take human error and hardware issues out of the equation?

[geordie666]

@sybenzvi: Yes, that's a great idea. I'll lean towards that approach.