Added new test suite and updated existing tests to verify always-both-attributes
behavior.
Changes:
- test_mean_median_display.py: NEW - Tests both attributes always present,
configurable state display, recorder exclusion, and config changes
- test_avg_none_fallback.py: Updated to test mean/median individually (65 lines)
- test_sensor_timer_assignment.py: Minor updates for compatibility (12 lines)
Coverage: All 399 tests passing, including new edge cases for attribute
presence and recorder integration.
