Adds sliding-window drift detector that compares cumulative path lengths
of visual odom and wheel odom over a configurable window (default 10 s).
Drift = |vo_path − wheel_path|; flagged when ≥ 0.5 m (configurable).
OdomBuffer handles per-source rolling storage with automatic age eviction.
Publishes Bool on /saltybot/vo_drift_detected and Float32 on
/saltybot/vo_drift_magnitude at 2 Hz. 27/27 pure-Python tests pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
