Switch to packaging

[flying-sheep]

This PR

• switches from the deprecated pkg_resources to packaging (Fixes Replace setuptools runtime dependency with packaging #337)
• changes CI so it actually installs runtime dependencies specified in the package metadata’s install_requires (instead of manually specifying setuptools)
• adds a pyproject.toml for a standards based build (instead of legacy convention based)

[flying-sheep]

FYI, you can change the workflow approval setting from

Fork pull request workflows from outside collaborators

• Require approval for first-time contributors who are new to GitHub
• Require approval for first-time contributors

to

Fork pull request workflows from outside collaborators

• Require approval for first-time contributors who are new to GitHub
• Require approval for first-time contributors

see https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/enabling-features-for-your-repository/managing-github-actions-settings-for-a-repository#controlling-changes-from-forks-to-workflows-in-public-repositories

[kmsquire]

Bump. It would be nice to get this in!

[askpatrickw]

Unfortunately, since this merge the GH Actions have been failing.
https://github.com/ekalinin/nodeenv/actions

[flying-sheep]

Seems like linting failures, should be easily fixable:

nodeenv.py:421:19: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
setup.py:16:1: E402 module level import not at top of file

No idea why I didn’t see those while authoring this PR.

/edit: ah, it’s because they didn’t exist when I wrote this PR. See #347 (comment)