fix: poetry run pytest raises SyntaxError: invalid escape sequence \S

[waketzheng]

Fixes #465

Checklist

• poetry run pytest
• pre-commit run --all-files
• tox

Motivation and Context

As the docopt project has been not maintained for many years, shall we to use another one to replace it:
docopt/docopt#507 (comment)
https://github.com/jazzband/docopt-ng

• Drop support for Python3.8
• Pass mypy check
• pre-commit autoupdate
• Remove coverage v5 from tox test list

[waketzheng]

@TheKevJames thanks for this useful and easy to use package～

Can this PR be accepted?

[jpmckinney]

+1 The test failures are only because CI isn't configured to allow third-party PRs to push results to Coveralls.

docopt is not maintained and has deprecated code that will eventually cause SyntaxError in all cases (it currently causes SyntaxWarnings, that are upgraded to errors if run with PYTHONWARNINGS=error or similar).

https://docs.python.org/3/whatsnew/3.12.html

A backslash-character pair that is not a valid escape sequence now generates a SyntaxWarning, instead of DeprecationWarning. For example, re.compile("\d+.\d+") now emits a SyntaxWarning ("\d" is an invalid escape sequence, use raw strings for regular expression: re.compile(r"\d+.\d+")). In a future Python version, SyntaxError will eventually be raised, instead of SyntaxWarning. (Contributed by Victor Stinner in gh-98401.)

[waketzheng]

@TheKevJames Cloud you take a look at this PR?