Use GitHub Actions.

[bdice]

Description

This PR overhauls our CI configurations to build and test signac with GitHub Actions. We've been planning to move to GitHub Actions for a long time and the breakage of our Windows builds (limited monthly minutes) and limited parallel runners are finally motivating a change here.

Before merging:

• Ensure we have builds for all supported platforms (Linux, macOS, Windows) and configurations (Python versions, oldest/newest dependencies). I'd like to see the following:
  • Linux, Python 3.10
  • Linux, Python 3.10 "minimal" (no optional dependencies)
  • Linux, Python 3.9
  • Linux, Python 3.8
  • Linux, Python 3.8 "oldest" (minimum versions of supported dependencies)
  • macOS, some supported Python version
  • Windows, some supported Python version
• Make an attempt at the "deploy to PyPI" logic that should release a source distribution (tarball) and a wheel tagged py3-none-any uploaded from one of those test configurations mentioned above. See https://github.com/pypa/gh-action-pypi-publish

Motivation and Context

I don't think an issue exists for this but we've been discussing moving to GitHub Actions for a while. cibuildwheel is a convenient and well-tested / easily configurable way to do so.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[bdice]

I hoped that cibuildwheel would let us easily test on multiple platforms even though signac is a pure Python package (no platform-specific parts of the wheel). Looks like CI fails:

cibuildwheel.util.NonPlatformWheelError: 
cibuildwheel: Build failed because a pure Python wheel was generated.

Based on pypa/cibuildwheel#1021, it looks like cibuildwheel is not an appropriate tool for testing multiple platforms with a pure wheel.