CI: run pytest across full matrix, not just 3.14

[martinkersner]

Finding

.github/workflows/python-package.yml:35 guards the pytest step with if: matrix.python-version == '3.14', so the suite only ever runs on one interpreter; 3.10–3.13 run only black + flake8. This masked the pre-existing pytest-pep8 startup failure (#81) on every version except 3.14.

Done when

• pytest runs on all matrix entries (drop the if: guard, or otherwise exercise tests across 3.10–3.14), and the matrix is green.

Context

Surfaced during review of PR #82 (#82), which removes pytest-pep8. Noted as optional follow-up in #81.

[martinkersner]

Obsolete after #96 (commit a9097a8), which removed pytest from CI entirely — the workflow now runs only black + flake8, and tests are run locally because they hit live prod endpoints. The if: matrix.python-version == '3.14' guard this issue references no longer exists, so there is nothing to fix. Closing as no longer applicable.