fix: report teardown failures as failed tests

[gchan]

Note: This PR replaces #85, which was rebased onto main but encountered GitHub PR state issues. This contains the same fixes with conflict resolution.

Summary

• Fixture teardown failures are now correctly reported as failed tests
• Previously, only setup and call phase outcomes were captured, so teardown failures would leave a test marked as "passed"
• Fixed ValueError when accessing xdist options without pytest-xdist installed

Fixes #84

Changes

1. Report teardown failures

The condition in pytest_runtest_logreport now handles teardown failures the same way it handles setup failures - capturing them to override the test result.

# Before
if report.when == 'call' or (report.when == 'setup' and report.failed):

# After  
if report.when == 'call' or (report.when in ('setup', 'teardown') and report.failed):

2. Fix xdist option access when xdist not installed

The numprocesses option only exists when pytest-xdist is installed. Previously, config.getoption("numprocesses") was called unconditionally, causing a ValueError when xdist wasn't present.

Rebase Details

This PR was rebased onto main which included PR #83 (tag-filters feature). A conflict occurred in __init__.py where both PRs attempted to fix the same xdist bug:

• PR Add --tag-filters option to filter tests using execution_tag marker #83's approach: Added default parameter to getoption("numprocesses", None)
• This PR's approach: Check if xdist plugin exists before calling getoption()

We chose this PR's approach as it's more explicit and avoids calling getoption() when the plugin isn't available.

Test status: All 75 tests passing ✅

Test Plan

• Added test test_pytest_runtest_logreport_fail_exception_in_teardown that verifies teardown failure overrides a passed call result
• All existing tests pass (75 total after rebase)
• Tests run without error when xdist is not installed

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Original work by @jimsynz in #85