fix: honor fail-on-flaky with xdist workers

[harbinresearcher]

Closes #386.

With --reruns 1 --fail-on-flaky, a test that fails once and then passes returns exit code 7 in serial execution, but returns 0 under pytest-xdist. The controller's session.items is empty, so the existing exit-status check cannot see the worker's repeated execution.

Record rerun reports on the controller through the existing XDistHooks instance and honor that state in pytest_sessionfinish. Keep the existing nonzero-exit guard and serial item check. No socket protocol, retry-selection, or public API changes.

Extend the existing exit-status tests across serial, one-worker and two-worker execution, including both CLI/marker reruns, tests that pass immediately, permanent failures, and a test skipped on its second attempt. Add the required changelog fragment.

Validation:

• Focused matrix: original 6 failed/15 passed; patched 21 passed.
• Full Windows Python 3.12.14 and Linux Python 3.14.8, pytest 9.1.1/xdist 3.8.0: baseline 258 passed; patched 273 passed.
• Linux Python 3.10.22/pytest 8.2.1/xdist 3.8.0: baseline 243 passed, 1 failed, 14 skipped; patched 258 passed, the same 1 failed, 14 skipped. JUnit failure identities match. The existing test_only_rerun_ini_override expects a contiguous FRF progress line, while pytest 8.2.1 inserts a percentage before the last F; its outcome counts are correct in both runs.
• Linux Python 3.14.8 without xdist: baseline 248 passed, 10 skipped; patched 249 passed, 24 skipped. New parallel variants correctly skip when the optional plugin is absent.
• Required pinned pre-commit checks pass. Configured Sphinx HTML build succeeds with one warning.
• Isolated sdist/wheel builds pass. The wheel was installed into a separate target; its import path was verified and all 21 exit-status cases pass using that installed copy.
• towncrier check --compare-with origin/master and git diff --check pass.
• Independent automated review found no actionable issue and separately verified two workers without the terminal plugin, teardown recovery and crash recovery (exit 7), and flaky success alongside a persistent failure (exit 1). This is not human maintainer review.

Disclosure: prepared and verified by an autonomous AI coding assistant with the account owner's authorization. macOS, PyPy, free-threaded Python and the entire CI version matrix were not run locally.