Kinova Gen3 physical instability

**Which model is the issue affecting?**
[Kinova Gen 3](https://github.com/google-deepmind/mujoco_menagerie/blob/main/kinova_gen3/gen3.xml)

**What is the issue?**
The robot arm exhibited bouncing/violent oscillations immediately upon spawning in the MuJoCo sim, particularly in Joint 3 and Joint 7. This led to explosions where the arm would jitter uncontrollably even without external contact or control input. I demonstrate this in the posted video where I am just spawning the robot in a bare env. I am not sure what the actual values are supposed to be but I started playing around with the xml file and tuned the values until the robot became stable and I was able to control it via teleoperation as seen in the second video.

## My Solution:

### 1. Re-tuned Actuator Classes

- **Large Actuators:** Reduced $k_p$ from `2000` to **`500`** and $k_v$ from `100` to **`20`**.
- **Small Actuators:** Reduced $k_p$ from `500` to **`100`** and $k_v$ from `50` to **`2`** to match the low-inertia wrist links.

### 2. Joint Regularization

Added default properties to the `` tag to improve solver stability:

- **Armature (`0.1`):** Stability to high-frequency dynamics by providing inertia?
- **Damping (`1.0`):** Internal joint resistance?

### 3. Contact Exclusions

Added explicit exclusions to ignore self-collisions between physically connected/adjacent bodies:

```xml

```

I tried a combination of all of these fixes, but what I got to work is posted here.

[gen3_fixed.xml](https://github.com/user-attachments/files/24629315/gen3_fixed.xml)

**Is there any additional context you can provide (e.g., a spec sheet or a URDF to show a value mismatch)?**

https://github.com/user-attachments/assets/1f9e7d2c-d846-4198-86a3-b266b5ce4dfd

https://github.com/user-attachments/assets/5a310eea-2b87-41f1-a55a-e71f1b146cd1