String split is failing on Python 3.13

[moorepants]

The 3.13 builds failed on conda forge, see conda-forge/opty-feedstock#33

This is the traceback:

+ python betts2003.py
Traceback (most recent call last):
  File "/home/conda/feedstock_root/build_artifacts/opty_1725960370278/test_tmp/betts2003.py", line 59, in <module>
    prob = Problem(obj, obj_grad,
    return self.use_parent_doc(f, overridden)
           ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/home/conda/feedstock_root/build_artifacts/opty_1725960370278/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_p/lib/python3.13/site-packages/opty/direct_collocation.py", line 73, in use_parent_doc
    func.__doc__ = self._combine_docs(self.mthd.__doc__,
                   ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
                                      ConstraintCollocator.__init__.__doc__)
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/conda/feedstock_root/build_artifacts/opty_1725960370278/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_p/lib/python3.13/site-packages/opty/direct_collocation.py", line 80, in _combine_docs
    _, middle = coll_doc.split('Parameters\n        ==========\n        ')
    ^^^^^^^^^
ValueError: not enough values to unpack (expected 2, got 1)
WARNING: Tests failed for opty-1.3.0-py313h9c9eb82_1.conda - moving package to /home/conda/feedstock_root/build_artifacts/broken
Traceback (most recent call last):
  File "/opt/conda/lib/python3.10/site-packages/conda_build/build.py", line 3523, in test
    utils.check_call_env(
  File "/opt/conda/lib/python3.10/site-packages/conda_build/utils.py", line 404, in check_call_env
    return _func_defaulting_env_to_os_environ("call", *popenargs, **kwargs)
  File "/opt/conda/lib/python3.10/site-packages/conda_build/utils.py", line 380, in _func_defaulting_env_to_os_environ
    raise subprocess.CalledProcessError(proc.returncode, _args)
subprocess.CalledProcessError: Command '['/bin/bash', '-o', 'errexit', '/home/conda/feedstock_root/build_artifacts/opty_1725960370278/test_tmp/conda_test_runner.sh']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/conda/bin/conda-build", line 11, in <module>
    sys.exit(execute())
  File "/opt/conda/lib/python3.10/site-packages/conda_build/cli/main_build.py", line 589, in execute
    api.build(
  File "/opt/conda/lib/python3.10/site-packages/conda_build/api.py", line 209, in build
    return build_tree(
  File "/opt/conda/lib/python3.10/site-packages/conda_build/build.py", line 3727, in build_tree
    test(pkg, config=metadata.config.copy(), stats=stats)
  File "/opt/conda/lib/python3.10/site-packages/conda_build/build.py", line 3537, in test
    tests_failed(
  File "/opt/conda/lib/python3.10/site-packages/conda_build/build.py", line 3584, in tests_failed
    raise CondaBuildUserError("TESTS FAILED: " + os.path.basename(pkg))
conda_build.exceptions.CondaBuildUserError: TESTS FAILED: opty-1.3.0-py313h9c9eb82_1.conda

and it seems that this split() call isn't working:

    @staticmethod
    def _combine_docs(prob_doc, coll_doc):
        beg, end = prob_doc.split('bounds')
        _, middle = coll_doc.split('Parameters\n        ==========\n        ')
        return beg + middle[:-9] + '        bounds' + end