Make gaze smoothing and Kalman filter tuning configurable

[YuanEZhou]

Summary

This PR makes gaze prediction smoothing and Kalman filter tuning configurable through
webgazer.params.

Changes

• Adds configurable gaze smoothing window size via gazeSmoothingWindowSize
  • Default is now 8
  • Previous value was 4
• Adds configurable Kalman filter measurement noise via kalmanMeasurementNoise
  • Default is now 120
  • Previous value was 47
• Adds configurable Kalman filter process noise scale via kalmanProcessNoiseScale
  • Default is now 0.08
  • Previous value was 1 / 10
• Updates bundled www/webgazer.js and source maps accordingly
• Documents previous default values in src/params.mjs comments

Motivation

The previous smoothing and Kalman filter values were hardcoded, making it difficult to tune gaze
stability for different use cases. Exposing these values as parameters allows applications to reduce
jitter or latency depending on their needs.