The way I understand it, ab1 is a the raw output of the machine, has the chromatogram and information about the run. fas has an initial sequence call, scf has information about sequence quality and seq has a trimmed sequence based on the scf file.
I don’t know of any tool that allows you to interact with ab1 files in Julia (I might be wrong) and most tools are GUI’s that allow users to check the chromatograms manually and change base calls. I think it can be easy to parse for the calls and basically obtain and equivalent to the fas file, but to actually check the chromatograms you need a tool that will transform the base call, the time and the quality into the usual chromatogram you see in tools like Sequencer.
I’m no expert with BioJulia, but I get the impression most of the tools thus far allow you to work with files that are mostly text based, like FASTA and newer ones.