Improve switcher between calibration and RB

[stavros11]

Not sure if there is a duplicate issue for this, but basically solve the TODO here

qibocal/src/qibocal/cli/builders.py

Line 256 in b48a3f5

# TODO: find a better way to choose between the two parsers

The only issue with this is that if an error is raised for whatever reason (unrelated to RB) this exception will appear in the traceback and may confuse people who don't know what it is. It is not super urgent in the sense that something does not work, but we should keep in mind to fix it at some point.