NavCore-Pixhawk v2.0.0 — SR-ESKF & Aviation-Grade Safety

This is a major upgrade from v1.0.0. The biggest change is the core filter — I rewrote the ESKF to use Square-Root covariance factorization, which means the covariance matrix can never go numerically unstable during long GPS-denied flights. Previously we were using eigenvalue clamping as a hack to keep things stable, that's gone now.
Added RAIM integrity monitoring so the system can detect and exclude bad GPS measurements instead of blindly trusting them. Multi-Hypothesis Tracking handles the case where GPS jumps after a long outage — instead of trusting the jump immediately, the filter maintains shadow hypotheses and picks the best one.
On the sensor side, magnetometer now does continuous RLS hard/soft-iron calibration during flight, and there's a basic Terrain Relative Navigation module using the Livox point cloud matched against a DEM.
Quaternion integration was upgraded from first-order Euler to RK4, which reduces attitude drift at high angular rates. Measurement updates now use iterated EKF (IEKF) for nonlinear sensors like UWB and tight GPS.
Test suite expanded to 30+ tests including Monte Carlo validation, GPS outage recovery metrics, and NEES/NIS filter consistency checks.