Fix ModuleNotFoundError during pip install

[asavoy]

When trying to pip install crlibm, a ModuleNotFoundError appears, breaking the install.

The module not found is distutils.command.upload, which has been removed in setuptools' recently published version 75.0.0. That module is depended upon by this project's setup.py.

When the build dependencies haven't been declared, pip will follow this fallback behavior and fetch the latest version of setuptools, which from above is no longer compatible.

To fix the issue, this PR adds a minimal pyproject.toml file to declare a dependency on setuptools prior to the breaking version.

How to reproduce

# Must have Python 3.12 installed
python --version
# Python 3.12.1

# Create an empty Python virtual environment
python -m venv .venv

# Activate the virtual environment
source .venv/bin/activate

# Install crlibm, providing a local path to the git repo
pip install ../crlibm  # <-- this fails, see error below

# To test that the library installed correctly
python -c 'import crlibm ; print(crlibm.exp_ru(1))'
# Should print: 2.7182818284590455

Example error message

Processing /Users/alvin/Projects/pycrlibm
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [20 lines of output]
      Traceback (most recent call last):
        File "/Users/alvin/Projects/pycrlibm-sandbox/.venv/lib/python3.12/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 353, in <module>
          main()
        File "/Users/alvin/Projects/pycrlibm-sandbox/.venv/lib/python3.12/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 335, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/Users/alvin/Projects/pycrlibm-sandbox/.venv/lib/python3.12/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 118, in get_requires_for_build_wheel
          return hook(config_settings)
                 ^^^^^^^^^^^^^^^^^^^^^
        File "/private/var/folders/tb/wv_dy5_j309_plh4f12tg3hr0000gn/T/pip-build-env-ipu4bbgt/overlay/lib/python3.12/site-packages/setuptools/build_meta.py", line 332, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=[])
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/private/var/folders/tb/wv_dy5_j309_plh4f12tg3hr0000gn/T/pip-build-env-ipu4bbgt/overlay/lib/python3.12/site-packages/setuptools/build_meta.py", line 302, in _get_build_requires
          self.run_setup()
        File "/private/var/folders/tb/wv_dy5_j309_plh4f12tg3hr0000gn/T/pip-build-env-ipu4bbgt/overlay/lib/python3.12/site-packages/setuptools/build_meta.py", line 503, in run_setup
          super().run_setup(setup_script=setup_script)
        File "/private/var/folders/tb/wv_dy5_j309_plh4f12tg3hr0000gn/T/pip-build-env-ipu4bbgt/overlay/lib/python3.12/site-packages/setuptools/build_meta.py", line 318, in run_setup
          exec(code, locals())
        File "<string>", line 15, in <module>
      ModuleNotFoundError: No module named 'distutils.command.upload'
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× Getting requirements to build wheel did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.

Workaround

For projects that depend on crlibm while this fix hasn't been merged, I have found a workaround.

• Add setuptools<75.0.0 to your project dependencies (to install the version of setuptools prior to the breaking change)
• Use the --no-build-isolation flag when you do pip install or uv sync (to use build dependencies defined in your project rather than in each dependency)

Note that this is a very precarious workaround - it assumes all your dependencies can be built with the same build dependencies.

[asavoy]

I've updated the description with a temporary workaround for others that might be affected