DOC: install docs dependencies from pip to avoid proj warnings

[m-richards]

Closes #2683
This sidesteps the issue with proj warnings on readthedocs with mamba by installing with pip instead.

da319bb tries to just install pyproj with pip, but this also seems to produce the warning.

Edit: for some reason installing from requirements files seems to break images as martin noted below.

[martinfleis]

For some reason, the image outputs are broken (see https://geopandas--3263.org.readthedocs.build/en/3263/docs/user_guide/mapping.html). Not sure if it is related to these changes or not...

[martinfleis]

If I am looking right, the latest version has solved it without any side issues?

[m-richards]

Not at a computer but I thought the savefig images were still broken when I gave up but maybe I was looking at an old link

[martinfleis]

All looks okay on my side at the moment. So we can probably just clean this and merge.

[m-richards]

Alright, this should be good to go now. I also fixed some build warnings from https://readthedocs.org/projects/geopandas/builds/24422174/
not sure if PYDEVD_DISABLE_FILE_VALIDATION=1 is actually going to work, or if that only works as inline to a bash command.

Edit: 3 final warnings (besides the ipython debugger frozen modules warnings)

/home/docs/checkouts/readthedocs.org/user_builds/geopandas/checkouts/3263/doc/source/docs/user_guide/interactive_mapping.ipynb:13: WARNING: File not found: 'docs/reference/api/geopandas.GeoDataFrame.plot.html'
/home/docs/checkouts/readthedocs.org/user_builds/geopandas/checkouts/3263/doc/source/docs/user_guide/interactive_mapping.ipynb:13: WARNING: File not found: 'docs/reference/api/geopandas.GeoDataFrame.explore.html'
/home/docs/checkouts/readthedocs.org/user_builds/geopandas/checkouts/3263/doc/source/gallery/choropleths.ipynb:: ERROR: Anonymous hyperlink mismatch: 2 references but 1 targets.

The first two seem to work despite the errors - I guess they're relative paths into the outputs of sphinx build.

The third is some missing hyperlinks (and also a broken image) in the first cell of the choropleths notebook which is super old predates #1731 which is as far back as I looked. @martinfleis you've probably got the best idea of which icon / what webpage to link to for pysal / or we just replace the old stuff with a new link just to pysal.org

[m-richards]

the objects.inv isn't present for the stable tag, isn't present at the redirect without a tag either.

[m-richards]

this doesn't need to be here, but it's not exactly harmful, and might come in handy in future

[martinfleis]

I don't think this will happen. We have geopandas-base on conda-forge that does not pull pyproj but geopandas does and I am not aware of discussions that it should change.

[m-richards]

We have geopandas-base on conda-forge that does not pull pyproj

I'm not sure that's right - I opened #3293 because as I understand it geopandas-base does require pyproj right now.

I thought these both depended on geopandas-base only, but having a look again it seems they depend on geopandas directly, so I'll remove this comment then.