[WIP] Update saving options and remove fst references

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

I want to change a few things about it. First of all, I would like you to save all quarters files to a single parquet file (that would be a list of the quarters dataframes) when downloaded, lazy-load the needed columnes to create the panels and the variables necessarie. Other thing I would like to change is that I want the options of the function to receive a vector with the following composition: save_options = (TRUE, TRUE) - the default, in which you save all files as csv. If (FALSE, TRUE) - saves quarters and panels as parquet. If (TRUE, FALSE) - saves only the panels in csv. else If (FALSE, FALSE) - saves only the panels as parquet. When saving in parquet, it should be a list of the panels. fst will no longer be used. I want you to remove all mentions of the fst, be it on the documentation or in the code. I recommend you to not test the function as it may take a long time.

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