build: Require setuptools v42.0.0+ for stability

[matthewfeickert]

Description

Resolves #1774

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* setuptools releases prior to v42.0.0 had stability issues with
pyproject.toml or didn't support PEP 517 and so couldn't support
pyproject.toml.
   - c.f. https://www.python.org/dev/peps/pep-0517/

Co-authored-by: Henry Schreiner <[email protected]>

[codecov]

Codecov Report

Merging #1783 (d6ecd26) into master (3691236) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1783   +/-   ##
=======================================
  Coverage   98.12%   98.12%           
=======================================
  Files          64       64           
  Lines        4270     4270           
  Branches      683      683           
=======================================
  Hits         4190     4190           
  Misses         46       46           
  Partials       34       34           

Flag	Coverage Δ
contrib	26.25% <ø> (ø)
doctest	60.58% <ø> (ø)
unittests	96.18% <ø> (ø)

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