Replace darglint docstring linter

[mvadari]

darglint (one of the linters this project uses, for docstrings) is no longer really being maintained. The last update to the repo was 3 years ago.

Some replacement options (source):

• darglint2
  • Note: this is listed in the description, and was last updated last year, so not sure if it is a good choice

    Important: darglint2 is very slow compared to alternatives due to its parser design. darglint2 is only intended as a low-effort replacement for darglint for those old darglint users who need bugfixes and critical features but don't want to spend the trouble of migrating to a better alternative. See e.g. Another darglint replacement jsh9/pydoclint#9 for details.

• pydoclint

The best strategy is probably to migrate to darglint2 at first for a drop-in replacement, then migrate to pydoclint later.