Investigate using python bindings of sdformat instead of the `gz` command line

Starting from version 13, sdformat introduced [native Python bindings](http://sdformat.org/tutorials?tut=python_bindings&cat=developers&). It's worth investigating if we could just call this library (that depends only on sdformat) instead of requiring to find the entire Gazebo Classic or Gazebo Sim suite.

Few comments:

- I could not find any package in PyPI nor conda-forge, last time I tried I think I installed it from the OSRF repo.
- Relevant discussion in https://github.com/ami-iit/jaxsim/pull/89#issuecomment-1954590803

Start by reviewing the sdformat native Python bindings tutorial and locating where rod currently invokes the `gz` command-line tools. Check whether usable sdformat packages are available through the OSRF repository, PyPI, or conda-forge. Done means determining whether the binding can replace the current dependency and documenting the required packaging and implementation changes.

Written by the indexing model from the issue text.