fix: remove --use-pep517 flag from pip command

[orlevii]

Pull Request Check List

Resolves: #4399

[neersighted]

I think this PR is misguided at best. What's happening here is the pystan release archive is broken. It cannot be built in a PEP-517 environment, which is isolated by definition.

Try reproducing with the following (poetry and pip are both not involved in this build process, as we instead use build):

docker run --rm -i --entrypoint bash python:3.9 <<EOF
set -xe
curl -LO https://files.pythonhosted.org/packages/10/9f/dcecf31ac08842a675ec337a14439b37d75f6da42f034b1fd5eb90b10b84/pystan-2.19.1.1.tar.gz
tar xvf pystan-2.19.1.1.tar.gz
cd pystan-2.19.1.1
python -m pip install build
python -m build
EOF

While setuptools is compatible with PEP 517, checking that your dependencies are installed by importing them is non-standard and not supported. pystan's setup.py does this, and it breaks in the face of a modern build environment.
A wheel (for your platform) would partially solve this, but is not uploaded.

I would suggest migrating to a newer pystan which solves these build woes, or if that is not possible, vendoring the code and patching the checks out of setup.py. While building with classical setuptools (in a non-isolated environment) does technically not trigger this, Poetry is moving to PEP-517 installs only (as is pip in the future), and as such, I don't think this is an appropriate fix.

[github-actions]

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