Require python version 3.10 in isaaclab.sh

[steple]

Description

3.10 is required. When running on Ubuntu 24, I ran into trouble because Ubuntu 24 ships with 3.12. I was able to get isaaclab.sh to work with the following steps:

• Install a version of 3.10 (be careful, 3.12 must remain the default).
• Create a venv with 3.10, install isaac sim in the venv, then proceed to install isaac lab.
• The following changes to the script:
  • In extract_python_exe, check that we found the desired version.
  • Use the result of extract_python_exe everywhere to invoke python (outside of extract_python_exe itself).

Also, fixed a bug where we could consider the system python valid even if we counted 0 installed isaacsim-rl packages. We meant to check for >0 packages installed.

Disclaimer: Someone else please try this locally.

Fixes # (issue) - Let me know if you'd like me to enter one.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation - Documentation already calls out that 3.10 is required.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works - Not a feature.
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file - Not an extension.
• I have added my name to the CONTRIBUTORS.md or my name already exists there