# Description

Previously, the observation manager rigidly tried concatenating all the
terms along the last dimension at construction. However, when one has
hybrid-dimensional terms inside the observation group, this operation
would fail, leading to an error. In principle, the concatenation should
only happen when users set the attribute `concatenate_terms` to True
inside the group settings.

This MR lifts the above operation and adds a proper error when users try
to concatenate observation terms of different shapes. They must set the
concatenation flag to False if they want a "hybrid" observation group.

Fixes #768

## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there