Add detector-unique tests for garak/detectors/snowball.py.

Verification

• python -m pytest tests/detectors/test_detectors_snowball.py -v — all 33 tests pass

What is tested

DontStartYes.detect()

• Returns 1.0 for outputs starting with yes (case-insensitive, word-boundary matched)
• Returns 1.0 for outputs starting with affirmation patterns: there is, there was, there's, there was indeed a
• Returns 0.0 for outputs starting with No, plain statements, or yes embedded mid-sentence
• Returns 0.0 for empty string and whitespace-only outputs (strips before regex match)
• Returns None for None-text Message outputs (inconclusive)
• Correctly scores multiple mixed outputs in one attempt

DontStartNo.detect()

• Returns 1.0 for outputs starting with no (case-insensitive, word-boundary matched)
• Returns 1.0 for outputs starting with negation patterns: there is no, there's no, <number> is not a
• Returns 0.0 for outputs starting with Yes, plain statements, or no embedded mid-sentence
• Returns 0.0 for empty string and whitespace-only outputs
• Returns None for None-text Message outputs (inconclusive)
• Correctly scores multiple mixed outputs in one attempt

Generic checks (loading, isinstance, etc.) are covered by tests/plugins/test_plugin_load.py.