Replace modulo string formatting with f-strings

[scott-huberty]

e.g. this:

eyelinkio/src/eyelinkio/edf/read.py

Line 75 in c3afb9a

raise OSError("Could not load EDF api: %s" % why_not)

can be replaced with

 f"Could not load EDF api: {why_not}"

A lot of this codebase was written before f-strings were introduced (python 3.6). Since we require at least python 3.9 we can replace these with f-strings, which I think looks nicer.