SWE gain test refactoring #2609
Description
For the SWE instrument, we should look into their gain test file and how to handle that in the best way moving forward.
They have a final line in the file that goes into the "distant future" that is a repeat of the last line. That is needed for I-ALiRT data, but they don't want to use that for science data. One thought on this is that we could remove that final line, and then in I-ALiRT we would say "any time beyond the end of the time in the ancillary file gets the last value", and then in science we could say "don't ever extrapolate the data".
There is an issue with lots of reprocessing because the ancillary file has a "start_date" that is before the mission and it keeps getting appended to and thus causes a lot of reprocessing. We should think about how best to handle this case and whether we need to push harder on the instrument team to change filenaming, but I do see where they are coming from in wanting to keep that since the data does span that full range.