Split PyPI release into per-platform tag workflows with scm-pinned wheel publishing

[Copilot]

This changes the release path from a single tag-driven publish workflow to independent Linux/macOS/Windows wheel pipelines that each build, test, and publish on bare X.Y.Z tags. It also moves package versioning to setuptools-scm so tag builds publish the tag version consistently and reject mismatched wheel artifacts before upload.

• Per-platform release workflows

  • Replaced the monolithic release workflow with:
    • build.yml for Linux
    • build-macos.yml
    • build-windows.yml
  • Each workflow now follows build-wheel -> test-wheel -> publish
  • Publish is tag-gated and uses PyPI trusted publishing via OIDC
  • Added per-workflow concurrency and paths-ignore so platform pipelines rerun independently and avoid unnecessary CI burn

• Wheel-first release behavior

  • Build jobs produce cp312/abi3 wheel artifacts per platform
  • Test jobs install the built wheel into a clean venv on a separate runner image and run the test suite there
  • Publish jobs download only their platform artifacts and upload with skip-existing for idempotent reruns

• Versioning hardening

  • Switched pyproject.toml to scikit_build_core.metadata.setuptools_scm
  • Added setuptools-scm to build requirements and local_scheme = "no-local-version"
  • Injected SETUPTOOLS_SCM_PRETEND_VERSION_FOR_COMPAS_CGAL on tag builds so CI-side tree mutations cannot produce dev releases
  • Updated runtime version lookup to read installed package metadata instead of a hardcoded __version__

• Publish-time safety checks

  • Added an explicit guard that fails publish if no wheel artifacts were downloaded
  • Added a tag/version assertion so every wheel filename must match GITHUB_REF_NAME before upload

env:
  CIBW_ENVIRONMENT: SETUPTOOLS_SCM_PRETEND_VERSION_FOR_COMPAS_CGAL=${{ github.ref_type == 'tag' && github.ref_name || '' }}

- name: Assert wheel versions match the tag
  run: |
    for whl in dist/*.whl; do
      v=$(basename "$whl" | cut -d- -f2)
      [ "$v" = "$GITHUB_REF_NAME" ] || exit 1
    done

• Fixes pypi release on tag push #76