feat(jax): add JAX-MD interface (deepmodeling#5590)

## Summary
- add a JAX-MD adapter for DeePMD JAX models, including energy, force,
neighbor-list, and `as_jax_md` helpers
- add focused JAX tests for energy/force evaluation, dense neighbor
conversion, and real JAX-MD neighbor lists
- add a water JAX-MD smoke example using dpdata to read the LAMMPS data
file
- document the JAX-MD interface in the third-party integration docs

## Tests
- `ruff check .`
- `PYTHONPATH=. pytest source/tests/jax/test_jax_md.py -q`
- JAX-MD water smoke run on GPU

<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

* **New Features**
* Added JAX-MD support for DeePMD JAX models, including energy, force,
neighbor-list, and model-loading utilities.
* Added a new water simulation example that runs a short JAX-MD NVE
smoke test from the command line.

* **Documentation**
  * Added setup and usage guidance for the JAX-MD integration.
  * Included a new third-party package entry for JAX-MD in the docs.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: njzjz