Add VBRM extended object tracker

[FlorianPfaff]

Summary

• add a PyRecEst-style VBRMTracker/VbrmTracker for oriented elliptical extended-object tracking
• implement linear and constant-velocity prediction, variational-Bayes update, shape/extent accessors, inverse-gamma parameter access, and contour generation
• add regression tests covering initialization, orientation-aware extent, prediction, update, empty measurement handling, layout handling, and contour points

Notes

• The tests import from pyrecest.filters.vbrm_tracker directly. This avoids touching the broad package export file while main is moving; adding from pyrecest.filters import VBRMTracker can be a small follow-up if desired.
• The tracker requires a positive-definite measurement noise covariance because the VBRM update explicitly inverts the measurement noise matrix.

Testing

• Locally syntax-checked the new tracker and tests.
• Ran the new tests with a NumPy-backed PyRecEst shim in this environment.