Update pydantic version to 2.13

[rwb27]

This bumps the minimum version of Pydantic to 2.13, which should avoid an upstream bug in earlier versions.

Closes #283

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[rwb27]

@julianstirling do you have a reproducible example I can run (or add to the test suite) to verify that updating Pydantic does actually fix the bug? If you're happy we just need to update the requirement, I'm happy to merge as-is.

[julianstirling]

@julianstirling do you have a reproducible example I can run (or add to the test suite) to verify that updating Pydantic does actually fix the bug? If you're happy we just need to update the requirement, I'm happy to merge as-is.

The issue is that if we use ImportString to import a file that imports a file that doesn't exist. It reports that the first file doesn't exist, rather than the actual missing file. To unit test this we would need to monkeypatch the systempath. The test that checks this in Pydantic is:

def test_importstring_reports_internal_import_error(tmp_path, monkeypatch):
    # Create a module that exists, but fails to import due to missing dependency
    (tmp_path / 'my_module.py').write_text('import definitely_missing_dep_xyz\n\nclass MyClass:\n    pass\n')
    monkeypatch.syspath_prepend(tmp_path)

    adapter = TypeAdapter(ImportString)

    with pytest.raises(ValidationError, match="No module named 'definitely_missing_dep_xyz'"):
        adapter.validate_python('my_module.MyClass')

[rwb27]

The issue is that if we use ImportString to import a file that imports a file that doesn't exist. It reports that the first file doesn't exist, rather than the actual missing file.

This was surprisingly straightforward to do: I've already got a module of unimportable submodules used to test this, so I've added one specifically for this error. I think this is ready now, assuming the tests pass.

[rwb27]

I have run the newly-parametrized test with both pydantic~=2.13 (which is what we require) and pydantic==2.12. I can confirm that the older version does not pass the tests due to incorrect error messages, and the newer version does.