ci: [GMLP-10024] build macOS wheels for Gumloop package

[waiho-gumloop]

Summary

• build Gumloop's cp310-abi3 wheels for Linux, Intel macOS, and Apple Silicon macOS
• smoke-test each wheel using the existing Python bindings test
• aggregate successful matrix artifacts into the existing Artifact Registry publish step

Test plan

• uv run pytest tests/test_libsy_custom_classifier.py -q -o asyncio_mode=auto (10 passed)
• uv run pytest tests/test_dev_wheel_versioning.py -q (9 passed)
• YAML syntax validation
• git diff --check
• Confirm all three wheel matrix jobs pass in GitHub Actions

Existing baseline failures

• Full pytest: 558 passed, 31 skipped, 1 failure because test_prometheus_exposition.py still looks up upstream package metadata as nemo-switchyard after the fork renamed it to gumloop-nemo-switchyard.
• Full Ruff: existing import-order finding in switchyard_rust/__init__.py; this PR does not modify that file.

Linear: https://linear.app/gumloop/issue/GMLP-10024/build-macos-wheels-for-gumloop-switchyard-fork

[waiho-gumloop]

/devin review

[waiho-gumloop]

/devin review