Update ToO infrastructure to handle larger target files

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.