Unpin setuptools_scm upper bound in setup_requires

[Dodothereal]

Unpin setuptools_scm upper bound in setup_requires

Summary

setup.py pinned setuptools_scm to <10, which blocks installation whenever a
newer setuptools_scm (already released) is the only version available in the
environment. This PR removes the upper bound so any compatible setuptools_scm
release can satisfy the build requirement, as requested in the issue.

Fixes #206

Changes

• setup.py: changed setup_requires=['setuptools_scm<10'] to
  setup_requires=['setuptools_scm'] (removes the <10 pin).

No other version constraints on setuptools_scm exist in the repository
(setup.cfg and the requirements/ files pin only setuptools, not
setuptools_scm; there is no pyproject.toml).

Testing

The change is a single metadata dependency pin; it has no runtime/code effect.
I verified by repository-wide search (grep -rn "setuptools_scm" --include=...)
that this was the only place the version was pinned, so no other file needs
updating. The sandbox used to run build/test commands (sandbox-run) is
currently unable to start on this VM (bwrap: setting up uid map: Permission denied, confirmed by bin/sandbox-selftest), so I could not run
python setup.py sdist/bdist_wheel against setuptools-scm>=10 here. The
maintainer's earlier feedback in the issue notes that builds work with
setuptools-scm>=10; this PR simply removes the pin that prevented that.

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AI assistance disclosure

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[janluke]

The pin was added for a reason. I'll fix the issue (probably today) myself with a full project overhaul which I've postponed for too long.