Migrate tool settings from setup.cfg to pyproject.toml

[pepoluan]

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What do these changes do?

Practically all still-maintained projects are migrating to have a Single Source of Truth for their builds: pyproject.toml

This is in accordance with the guidelines in PEP518 and PEP621.

I have ascertained that all tools aiosmtpd uses -- both as dependency or for development -- now have support for putting their configuration in pyproject.toml (some needs a bit of workaround but works well). This left us with an empty setup.cfg file, which I removed because it's no longer useful (all setup information is now in pyproject.toml as well).

Are there changes in behavior for the user?

None if user has the latest pip and setuptools.

Related issue number

None.

Checklist

• [x] I think the code is well written
• [x] Unit tests for the changes exist
• [x] tox testenvs have been executed in the following environments:
  • [x] GitHub CI
• [x] Documentation reflects the changes
• [x] Add a news fragment into the NEWS.rst file

[codecov[bot]]

Codecov Report

Merging #363 (75cc9d5) into master (79c8671) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #363   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1706      1706           
  Branches       310       310           
=========================================
  Hits          1706      1706           

Impacted Files	Coverage Δ
aiosmtpd/__init__.py	100.00% <100.00%> (ø)

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[waynew]

@pepoluan FYI I'm still super interested in this getting in. There is a merge conflict in __init__.py. I've (re)reviewed PRs newer and up to this one, and will probably review more tomorrow afternoon.