Adds multi-pass spatial-Gaussian hole filler for D435i depth images.
Each pass replaces zero/NaN pixels with the Gaussian-weighted mean of valid
neighbours in a growing kernel (×1, ×2.5, ×6 default); original valid
pixels are never modified. Handles uint16 mm → float32 m conversion,
border pixels via BORDER_REFLECT, and above-d_max pixels as holes.
Publishes filled float32 depth on /camera/depth/filled at camera rate.
37/37 pure-Python tests pass (no ROS2 required).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
