Skip tearDown when setUp fails, and never let tearDown crash the worker

[kei-nan]

Summary

• _runTest called after_func() (tearDown) unconditionally in a bare finally, even when before_func() (setUp) raised. A tearDown written against a successful setUp (e.g. one that reads self.env) then raises its own exception -- typically AttributeError, since the attribute setUp would have assigned was never set. That second exception escaped _runTest uncaught: unlike the original setUp/test failure, it bypasses handleFailure entirely.
• In the parallel coordinator this kills the whole worker process instead of failing just the one test. Because RLTest schedules different methods of the same test class across different workers, a single flaky setUp (e.g. a transient env-startup connection refusal) can take down every worker in the pool near-simultaneously.
• Track whether setUp completed; skip tearDown if it didn't (mirroring the existing exit_on_failure branch's intent, generalized to the default path). If tearDown itself raises after a successful setUp, route it through handleFailure like any other test failure instead of letting it propagate.

Found while diagnosing a RediSearch nightly run where this exact pattern (TestBM25NormMax in test_scorers.py) hit all 4 parallel coordinator workers within ~2 seconds of each other and took the whole "Flow tests (coordinator)" CI step down for the full 120-minute timeout: https://github.com/RediSearch/RediSearch/actions/runs/36269638134/job/108481212637

Test plan

• Added tests/unit/test_teardown_after_failed_setup.py reproducing both: (1) setUp fails -> tearDown must be skipped, not crash; (2) setUp/test succeed but tearDown itself raises -> must be reported via handleFailure, not propagated.
• Verified both new tests fail with an unhandled exception against the unpatched code, and pass with the fix.
• Full unit suite (pytest tests/unit/) passes: 161 passed, 5 skipped.

🤖 Generated with Claude Code

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Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 46.60%. Comparing base (02cfbb9) to head (7d69fcc).
⚠️ Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
RLTest/__main__.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #257       +/-   ##
===========================================
+ Coverage   32.46%   46.60%   +14.14%     
===========================================
  Files          17       18        +1     
  Lines        2597     2755      +158     
===========================================
+ Hits          843     1284      +441     
+ Misses       1754     1471      -283     

Flag	Coverage Δ
unittests	46.60% <90.90%> (+14.14%)	⬆️

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