[FEATURE] Improve type annotation (and documentation?) for `TriangleMesh.at` indexing methods

### Terms - [x] Checked the [existing issues](https://github.com/jeertmans/DiffeRT/issues?q=is%3Aissue+label%3Aenhancement) to see if my suggestion has not already been suggested; ### Description Currently, the `TriangleMesh.at` methods, such as `add`, do not provide information about the accepted keyword arguments. I'm not sure if it's feasible or worth the hassle, but wouldn't it be nice to automatically derive allowed keyword arguments (and maybe their documentation) from `jax.numpy.ndarray.at.get`? ### Screenshots <img width="575" height="89" alt="Image" src="https://github.com/user-attachments/assets/fca284ef-ccbb-4af8-b013-af6e47862cbc" /> <img width="575" height="89" alt="Image" src="https://github.com/user-attachments/assets/f8783881-26db-444e-b93d-532a31144846" /> ### Additional information https://docs.jax.dev/en/latest/_autosummary/jax.numpy.ndarray.at.html