Update strings to be more pythonic - use f-strings

[intendo]

Update all strings to use f-strings rather than using str.format syntax

[sobolevnrm]

@speleo3 @orbeckst -- I think one of you suggested this before. Do you concur?

[IAlibay]

Probably worth mentioning this, some very small parts of the codebase now use f-strings as of #85 and #84.

May I suggest taking a strategy where type hinting & f-strings are added progressively as API docs are completed (say for something like #98)?

[speleo3]

I like f-strings and certainly use them in new code when possible. But updating existing code with a new pattern is usually low priory for me and it comes with an inherit risk for regressions.

[intendo]

Closing issue due to lack of progress and I agree with @speleo3 and @IAlibay that this can be done incrementally over time.