ltfs_ordered_copy QoL features (type annotations, etc.)

[talpid]

Is your feature request related to a problem? Please describe.
Not a problem per se, rather a minor inconvenience (and offer for contribution): the ltfs_ordered_copy script lacks several "creature comforts"/conveniences found in modern python modules (e.g.: type annotations) - I assume this is with a view to maximising compatibility.

Describe the solution you'd like
Without knowing the appetite of the maintainers for breaking compatibility with older python versions (and/or introducing an entirely new script with greater minimum python version requirements - messy IMHO), the following solutions could be considered:

• (non-breaking) a low-friction solution for type annotations specifically would be a stub file.
• (non-breaking) adding docstrings (optionally with an established style, e.g.: numpy) aids readability.
• (breaking) if a (new) minimum version can be established, various other readability improvements enabled by in-language features (e.g.: f-strings, more concise/readable variants of standard library functions (such as those in pathlib)) could be implemented.

Describe alternatives you've considered
The above are three "alternatives" (non-mutually-exclusive) I've considered; a fourth would be "do nothing". I personally plan to utilise some of the classes within my own work, so will likely invest effort "modernising" regardless - while I could hypothetically maintain a fork of this entire repository for the sake of one script, this overhead is a disincentive, and realistically other users are unlikely to stumble across such a fork; including modernising updates in the upstream makes this work available to a broader user base.

[talpid]

Additional consideration (writing as I've now begun the process of digging into this to utilise the classes elsewhere): even a minor refactor to control evaluation (so the file may be used as a module vs. only as a script, via if __name__ == "__main__") would be a great improvement.

For my (currently only internal; happy to share per OP) draft I've broken out the lines after # Start program here into parse_args(), configure_logging(args) and main() functions; this allows users to access the classes without executing the script, and also substitute either own logging (and/or main) functionality as needed.

[piste-jp]

It's based on the product planing. When we drop supports of ancient OSs.