# Description

Previously the root positions was obtained by performing the following
steps:

1. Call PhysX getters to get transforms and velocities
2. Concatenating the two to make a single state tensor
3. Indexing this tensor to get the position

For applications where we only want the positions, the above is an
expensive operation as we call CUDA-MemCpy twice and then do
concatenation which adds overhead.

This MR simplifies the above process by having separate lazy buffers for
poses, velocities and states.

Fixes # (issue)

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## Type of change

- New feature (non-breaking change which adds functionality)
- Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- This change requires a documentation update

## Screenshots

Please attach before and after screenshots of the change if applicable.

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## 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
- [ ] 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

---------
Signed-off-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>