Installing "sdist + patches" is not supported by Python package infrastructure.

We review existing patches, and for those packages that still need them, we create a repository fork and create and deposit an sdist tarball from here.

Tickets:

• rst2ipynb: Remove patches after update to 0.2.3 #31967/IPython/Jupyter upgrade for Sage 9.5 #31280 rst2ipynb: Update to 0.2.3 to remove patching
• setuptools: Upgrade to 58.2.0, remove old easy_install patch #32691 setuptools: Upgrade to 58.2.0, remove old easy_install patch
• cython: Eliminate use of custom patches #32832 cython: Eliminate use of custom patches
• pyzmq: Fix build errors; zeromq, pyzmq: Update; setuptools: upgrade to 59.2.0 #32828 pyzmq

Packages with patches can be found as follows:

$ ./sage -package list --has-file install-requires.txt --has-file patches | sort
cvxopt
cypari
cython
dot2tex
ipywidgets
notedown
numpy
pillow
psutil
rpy2
setuptools
sphinx
widgetsnbextension

Also, some Python packages need specific settings of environment variables at build time. Example: #21170 (pypolymake); a new package script such as spkg-env could set these (#29045)

Finally, some packages may install custom configurations, such as the notebook package's jupyter_notebook_config.py that currently gets installed into "$SAGE_INST_LOCAL"/etc/jupyter.

CC: @dimpase @orlitzky @tobiasdiez

Component: build

Issue created by migration from https://trac.sagemath.org/ticket/31543