Installing environments via pixi fails

1. Currently the tag used for environments is not recognised by pixi and needs to be modified to `tool.pixi.environments` instead of just `environment`. Throws error,
```
⚠ The feature 'drake' is defined but not used in any environment
╭─[/home/wslaniakea/git/comodo/pyproject.toml:78:20]
77 │
78 │ [tool.pixi.feature.drake.pypi-dependencies]
· ─────
79 │ drake = ">=1.34.0, <2"
╰────
help: Remove the feature from the manifest or add it to an environment

⚠ The feature 'hippopt' is defined but not used in any environment
╭─[/home/wslaniakea/git/comodo/pyproject.toml:86:20]
85 │
86 │ [tool.pixi.feature.hippopt.dependencies]
· ───────
87 │ liecasadi = "*"
╰────
help: Remove the feature from the manifest or add it to an environment

Error:
× unknown environment 'drake'
```

2. Installing the env throws `ffmpeg-python` not found error since there is a typo
```
× failed to solve the conda requirements of 'default' 'linux-64'
╰─▶ Cannot solve the request because of: No candidates were found for ffmepg-python *.
```

3. Running the jaxsim examples cause error that `integrators` cannot be imported. Removing the import since its not used fixes this issue.

Start with pyproject.toml around the environment declarations and dependency entries identified in the error output, then inspect the jaxsim examples for the unused integrators import. Verify the environment installs without the reported pixi and ffmepg-python errors, and confirm the examples run successfully; an open linked pull request already tracks this work.

Written by the indexing model from the issue text.