Adjust for NumPy 2.0.0

[khaeru]

With the release of NumPy 2.0.0, we see failures of the "pytest" GitHub Actions workflow, like here:

=========================== short test summary info ============================
FAILED genno/tests/compat/test_compat.py::test_import_pyam - AttributeError: `np.string_` was removed in the NumPy 2.0 release. Use `np.bytes_` instead.. Did you mean: 'strings'?
FAILED genno/tests/core/test_computer.py::test_require_compat - AttributeError: `np.string_` was removed in the NumPy 2.0 release. Use `np.bytes_` instead.. Did you mean: 'strings'?
FAILED genno/tests/core/test_exceptions.py::test_computationerror_ipython - KeyError: 'evalue'
FAILED genno/tests/test_operator.py::test_unique_units_from_dim[attrseries] - AssertionError: Regex pattern did not match.
 Regex: "Non-unique units \\['kg', 'km'\\] for .* 'Baz'"
 Input: "Non-unique units [np.str_('kg'), np.str_('km')] for AttrSeries 'Baz'"
FAILED genno/tests/test_operator.py::test_unique_units_from_dim[sparsedataarray] - AssertionError: Regex pattern did not match.
 Regex: "Non-unique units \\['kg', 'km'\\] for .* 'Baz'"
 Input: "Non-unique units [np.str_('kg'), np.str_('km')] for SparseDataArray 'Baz'"
FAILED genno/tests/core/test_quantity.py::TestQuantity::test_ffill[sparsedataarray] - ImportError: numpy.core.multiarray failed to import
ERROR genno/tests/compat/test_pyam.py - AttributeError: `np.string_` was removed in the NumPy 2.0 release. Use `np.bytes_` instead.. Did you mean: 'strings'?
ERROR genno/tests/compat/test_pyam.py - AttributeError: `np.string_` was removed in the NumPy 2.0 release. Use `np.bytes_` instead.. Did you mean: 'strings'?

These appear to be:

1. "AttributeError: np.string_ was removed" → pandera not compatible with numpy 2.0 unionai-oss/pandera#1656 (duplicate) via ixmp4 and pyam-iamc.
   • pyam-iamc 2.2.3 was released with Pin numpy<2.0 IAMconsortium/pyam#861 that restricts numpy < 2 in the package dependencies, perhaps for this reason.
2. "ImportError: numpy.core.multiarray failed to import" → ImportError: numpy.core.multiarray failed to import with NumPy 2.0.0 pydata/bottleneck#453. This appears to occur only when doing SparseDataArray.ffill().
   • Bottleneck 1.4.0 was released 2024-06-18.
   • Confirmed fixed via Adjust for NumPy 2.0.0 #141.
3. Others: these fail because np.str_ instead of ordinary Python str are compared.

See also numpy/numpy#26191 for the status of other packages.

Fix for (3):

• Adjust the code.

Mitigations for (1), (2)—some or all of:

• Exclude NumPy 2.0.0 from CI.
• Warn in docs, linking to this issue.
• Wait for the upstream projects to fix those issues and make new releases.
• Remove the work-around/mitigation.

[khaeru]

1. "AttributeError: np.string_ was removed" → pandera not compatible with numpy 2.0 unionai-oss/pandera#1656 (duplicate) via ixmp4 and pyam-iamc.
   • pyam-iamc 2.2.3 was released with Pin numpy<2.0 IAMconsortium/pyam#861 that restricts numpy < 2 in the package dependencies, perhaps for this reason.

• The pandera issue was resolved upstream.
• pyam-iamc 2.2.4 was released with Remove numpy pin IAMconsortium/pyam#871 removing the pin, so it is no longer necessary to override it in the genno CI workflow.