Add innovation gating and consistency metrics (NIS/NEES)

[jbrodovsky]

Context

Robust navigation requires rejecting bad measurements and monitoring filter consistency over time.

Scope / Requirements

• Compute innovation and NIS for each measurement update; gate using chi-square thresholds.
• Support configurable behaviors: reject measurement, down-weight, or robust loss (e.g., Huber).
• Compute NEES when ground truth is available and log to CSV alongside navigation outputs.
• Expose configuration options in CLI/config files.

Acceptance Criteria

• Outlier measurements are flagged and do not destabilize the filter.
• NIS/NEES time series can be exported with the navigation solution.
• Unit tests cover gating logic and threshold handling.