Make test_tests_collected_once actually verify coverage

[adamtheturtle]

Summary

• The custom linter test `test_tests_collected_once` was passing vacuously: `capsys` could not see the inner `pytest.main` output, and the nested run was also exiting with `INTERNAL_ERROR` because of `pytest-retry`, so 0 items were ever collected. Replaced the stdout-parsing approach with a small pytest plugin that records collected node IDs directly, and disabled `pytest-retry` in the nested run (matching the existing workaround in `test_ci_patterns_valid`). Removed a stray `breakpoint()` and added `assert all_tests` as a sanity check.
• Added the missing test files and docs (`ci/test_custom_linters.py`, `tests/mock_vws/test_respx_mock_usage.py`, `tests/mock_vws/test_target_validators.py`, `docs/source/httpx-example.rst`) to the CI matrix in `.github/workflows/test.yml` — these were the real coverage gaps the now-working linter test surfaced.

Test plan

• `uv run pytest ci/test_custom_linters.py` passes locally.

🤖 Generated with Claude Code

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Note

Low Risk
Low risk: changes are limited to CI configuration and a custom linter test that validates pytest collection patterns; main risk is CI runtime/flake if pytest plugin interactions differ across environments.

Overview
Fixes the custom CI linter so it actually validates test coverage across the CI matrix. ci/test_custom_linters.py now collects tests via a lightweight pytest plugin (pytest_itemcollected) instead of parsing captured stdout, disables pytest-retry in the nested pytest.main run to avoid internal errors, and adds a sanity assert all_tests.

Closes CI coverage gaps. The workflow matrix in .github/workflows/test.yml is updated to include previously-missed patterns (additional mock VWS tests, ci/test_custom_linters.py, and the docs/ tree), and pyproject.toml adds pytest_itemcollected to Vulture’s ignore list to avoid false positives.

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