move build configuration into `pyproject.toml`

[zacharyburnett]

in line with PEP621, with the new setuptools; this also future-proofs against uses of a PEP517 build like in the new Tox update

[zacharyburnett]

converting to draft to work on building C extension under PEP517; should be tested with #218

[codecov[bot]]

Codecov Report

Base: 87.17% // Head: 87.17% // No change to project coverage :thumbsup:

Coverage data is based on head (29afd93) compared to base (78cca9f). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #216 +/- ## ======================================= Coverage 87.17% 87.17% ======================================= Files 17 17 Lines 1333 1333 ======================================= Hits 1162 1162 Misses 171 171 ``` | Flag | Coverage Δ | | |---|---|---| | unit | `87.17% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#carryforward-flags-in-the-pull-request-comment) to find out more. Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope)

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[zacharyburnett]

temporarily reverting this PR due to suspected involvement in https://jira.stsci.edu/browse/SPB-1432