fix: resolve coverage config relative to pytest's rootdir (#692)

[DawnofGenX]

Problem

Coverage resolves a relative config_file (the default .coveragerc, plus the
pyproject.toml / setup.cfg / tox.ini fallbacks) and a relative data_file
against the current working directory. Running pytest from a subdirectory
therefore silently ignores the project's coverage configuration:

# pyproject.toml at the project root
[tool.coverage.report]
exclude_also = ['def __repr__']

• cd project && pytest tests/ → exclude_also applies (100%).
• cd project/tests && pytest . → exclude_also is ignored, and .coverage
  is written into tests/ rather than the project root.

Changes

Pass pytest's rootdir through to the controllers and use it as the anchor for
coverage's config/data lookup. It only differs from the cwd in exactly the case
that is broken (running from a subdirectory), so root-level invocations are
unaffected. An explicit --cov-config still wins.

Verification

• New test test_config_at_rootdir_used_from_subdirectory fails on main
  (the excluded line is reported missing) and passes with the fix.
• Full suite in a clean environment: 206 passed, 3 skipped. The only failure,
  test_celery, is pre-existing here (celery is not installed) and fails
  identically on main.