Enforce the existing 100% coverage of scs/py/__init__.py in CI

[tschm]

Subcategory: test coverage & depth
Current → target: 8 → 10

Problem

The Python layer is fully covered, but nothing in CI measures it, so a regression would be
invisible.

Measured locally (run from outside the repo so the source mapped to the installed module):

Name                                    Stmts   Miss  Cover
----------------------------------------------------------
site-packages/scs/__init__.py             114      0   100%
----------------------------------------------------------
TOTAL                                     114      0   100%
396 passed, 67 skipped

But grep -n "coverage\|--cov" .github/workflows/*.yml pyproject.toml returns nothing:
no workflow installs pytest-cov, passes --cov, or enforces a threshold. The value is
100% today by accident of discipline, not by enforcement.

Files / config to change

• add pytest-cov to the test job's dependency list in .github/workflows/build.yml
  (or freethreading_tests.yml, whichever is the canonical test job)
• run pytest --cov=scs --cov-report=term-missing --cov-fail-under=100

Note: this measures the Python layer only. The ~1,300-line C wrapper in scs/scsobject.h
has no coverage measurement; that is out of scope for this issue.

Done when

At least one CI job enforces a coverage threshold on scs/py/__init__.py, and dropping a
line of its coverage fails a pull request.

[bodono]

Thanks. We're not going to add a 100% coverage gate on the Python layer. It's a small file, and a hard threshold tends to generate churn rather than catch bugs. Closing as not planned.