[BUG] Rest Stability of the Bending Model Applied in VBDIntegrator

[AnkaChan]

Bug Description

The bending model that VBDIntegrator is currently using does not have rest stability. If we fix a single vertex, and let a model fall freely, the currently bending model can cause angular momentum injected to the system, as shown in the screen capture:

We need to revisit the bending model and write more through test to make sure that our bending model is artifact-free.

System Information

No response