Setuptools should be a dependency

[kaimast]

If it is not installed, I get

  File "/home/kai/dev/pyenv/lib/python3.12/site-packages/geni/aggregate/apis.py", line 137, in createsliver
    from ..minigcf import amapi2 as AM2
  File "/home/kai/dev/pyenv/lib/python3.12/site-packages/geni/minigcf/amapi2.py", line 14, in <module>
    from .util import _rpcpost
  File "/home/kai/dev/pyenv/lib/python3.12/site-packages/geni/minigcf/util.py", line 13, in <module>
    from .. import _coreutil as GCU
  File "/home/kai/dev/pyenv/lib/python3.12/site-packages/geni/_coreutil.py", line 13, in <module>
    import pkg_resources
ModuleNotFoundError: No module named 'pkg_resources'

It might also be good to transition to a pyproject.toml file at some point.

[nbastin]

We definitely need to switch the build system to use pyproject.toml, since we sadly have no choice. If you have thoughts and want to send a PR that makes some choices and solves that, that would be great, otherwise I'll try to get to it over winter break.