CI: build (3.14) fails — pytest-pep8 incompatible with modern pytest

[martinkersner]

Summary

build (3.14) in .github/workflows/python-package.yml fails at pytest startup, before any test is collected. Pre-existing on main (e.g. run on main@2f3050f, 2026-06-04) — not introduced by any open PR. The 3.14 job is the only matrix entry that runs pytest (if: matrix.python-version == '3.14', line 35); 3.10–3.13 run only black + flake8, so they stay green and mask this.

Error

pluggy._manager.PluginValidationError: Plugin 'pep8' for hook 'pytest_collect_file'
hookimpl definition: pytest_collect_file(path, parent)
Argument(s) {'path'} are declared in the hookimpl but can not be found in the hookspec

Root cause

requirements/requirements-test.txt pins pytest-pep8>=1.0.6 — an abandoned plugin (last release ~2014) whose pytest_collect_file(path, parent) hook uses the path argument that modern pytest removed from the hookspec. On Python 3.14, pip resolves a current pytest/pluggy that rejects the legacy plugin, so pytest aborts at startup.

Proposed fix (decide during impl)

• Preferred: remove pytest-pep8 from requirements/requirements-test.txt. It's dead weight — flake8 (7.3.0) already runs as its own CI step and covers pep8/style; nothing invokes the --pep8 flag, and the pytest call is a plain python -m pytest tests/.
• Alternatives (worse): pin pytest<8.4 (likely unsatisfiable on 3.14), or swap to pytest-flake8 (also unmaintained).

Done when

• build (3.14) runs the test suite to completion (green) on a branch based on main (not on any in-flight feature PR).
• No abandoned pytest plugin remains in requirements-test.txt.

Notes

• Base the fix branch on origin/main, independent of PR snake_case query params: send top_n / min_volume_usd #80 (snake_case params, Bisonai/datamaxi-backend#7398) — that PR's red 3.14 check is this same pre-existing failure, not its own regression.
• Optional follow-up worth considering: the if: matrix.python-version == '3.14' guard means tests only ever run on one interpreter; consider running pytest across the whole matrix once it's green.