Bump up shonan optimality threshold param

This commit passes in the optimality treshold explicitly from GTSFM: a value of `-1e-5` compared to `-1e-4` default value.
I tried using 0 and `1e-5` (value used in paper for large datasets) but even the unit tests are taking up a lot of time with higher thresholds.

gtsfm/averaging/rotation/shonan.py

@@ -35,6 +35,9 @@
 
 _DEFAULT_TWO_VIEW_ROTATION_SIGMA = 1.0
 
+# The threshold for the smallest eigenvalue check in GTSAM. Defaults to -1e-4 in GTSAM.
+_OPTIMALITY_THRESHOLD = -1e-5
+
 
 class ShonanRotationAveraging(RotationAveragingBase):
     """Performs Shonan rotation averaging."""
@@ -66,6 +69,7 @@ def __get_shonan_params(self) -> ShonanAveragingParameters3:
         shonan_params = ShonanAveragingParameters3(lm_params)
         shonan_params.setUseHuber(True)
         shonan_params.setCertifyOptimality(False)
+        shonan_params.setOptimalityThreshold(_OPTIMALITY_THRESHOLD)
         return shonan_params
 
     def __measurements_from_2view_relative_rotations(