fix: report teardown failures as failed tests

[jimsynz]

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"

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. This was breaking CI.

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 (63 total)
• Tests run without error when xdist is not installed

[gchan]

@jimsynz this looks great. Could you please resolve the conflict as result of a recent merge. Context: https://github.com/buildkite/test-collector-python/pull/83/changes#r2715206637

I'm going to prepare a new release of the collector to add support for #83 , so it would be great to get this in too!

[gchan]

Closing in favor of #86 which contains the rebased commits with conflict resolution. See the new PR for details on the rebase and merge conflict resolution.