{BugFix} Fix sign of the magnetometer rectification matrix

Summary:
Fix sign -- Determinant of the matrix should remain positive (calibration convention that the codebase enforce here https://github.com/facebookresearch/projectaria_tools/blob/14ab31d2e476f401744e0de338392f9c885013e3/core/calibration/loader/SensorCalibrationJson.cpp#L118)

A proper fix, would be to flip the sign only if the determinant is negative, I assume ... and will come later

Differential Revision: D85268025

fbshipit-source-id: 5612de5ec68035dd9dc133afa1d0b1ef4fdc749b

Author: SeaOtocinclus

core/calibration/loader/DeviceCalibrationJson.cpp

@@ -267,7 +267,7 @@ nlohmann::json magnetometerCalibrationToJson(
   // 3. `biasFromJson`: Gen1: muT -> T, Gen2: Gauss -> T.
   double biasScale = deviceVersion == DeviceVersion::Gen1 ? 1e-6 : 1e-4;
 
-  Eigen::Matrix3d magMatForJson = -magMat.inverse() * rectificationMatrixScale;
+  Eigen::Matrix3d magMatForJson = magMat.inverse() * rectificationMatrixScale;
   Eigen::Vector3d biasForJson = biasInTesla / biasScale;
 
   magJson["SerialNumber"] = "";