Miscellaneous updates for 2023-W15

[khaeru]

Housekeeping items:

• Replace usage of deprecated pkg_resources with importlib.metadata.
• Remove codecov from ixmp[tests] optional dependencies.
  • This package was long ago deprecated (1, 2) and we stopped using it at the time, but it remained in the dependencies. Now, however, the package has been entirely deleted from PyPI, without prior announcement, which means pip is not able to satisfy requirements for ixmp[tests] for any released version. All released versions of ixmp are now uninstallable. Per Codecov disappeared in PyPI? codecov/python-standard#31 (also 3, 4) this appears to have broken other code as well.
  • With this PR merged, CI workflows for downstream packages (message-ix, message-ix-models, message-data) can pip install "ixmp @ git+https://github.com/iiasa/ixmp.git@main" to work.
  • We can wait for codecov to be re-created on PyPI (per link 4, above) or, if this does not occur soon, we can proceed to release ixmp 3.7.0.
• Use pyproject.toml for packaging, instead of setup.{cfg,py}.

How to review

Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation. N/A
• Update release notes. N/A

[codecov]

Codecov Report

Merging #476 (fb2e746) into main (e490f48) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #476   +/-   ##
=====================================
  Coverage   98.5%   98.5%           
=====================================
  Files         42      42           
  Lines       4486    4489    +3     
=====================================
+ Hits        4422    4425    +3     
  Misses        64      64           

Impacted Files	Coverage Δ
ixmp/__init__.py	100.0% <100.0%> (ø)

[glatterf42]

Looks good to me except for two minor things in pyproject.toml:

1. The email supplied for the authors of our project doesn't exist anymore (as far as I know)
2. Is there any reason to supply only http links for the repository and documentation instead of https?

[khaeru]

Looks good to me except for two minor things:

1. The email supplied for the authors of our project doesn't exist anymore (as far as I know)

Good catch. Which should we now prefer? I guess we could remove the e-mail altogether and instead give our own in the "maintainers" field…

2. Is there any reason to supply only http links for the repository and documentation instead of https?

No, thanks. I will correct this.

[glatterf42]

I don't know if we have any other official address. But giving ours as the maintainers also sounds good.

[khaeru]

Okay, done! Please ✅ if we're good to go.