doc: update pictures in documentation

### Describe the enhancement requested

At the moment pictures illustrate that vertex chunks are named `part0`, `part1`, etc., while they are actually named `chunk0`, `chunk1`, etc.

<img width="780" height="432" alt="Image" src="https://github.com/user-attachments/assets/ddd56d65-9361-4aab-bb7e-9158b755cdfd" />

I'm afraid it may be confusing for users.

### Component(s)

Documentation