Add reusable demo utilities and DemoBase lifecycle class

[yuecideng]

Description

This PR introduces a shared demo utility layer for simulation scripts and refactors the six scripts/tutorials/atomic_action/ tutorials to use it.

New components:

• embodichain.lab.sim.utility.demo_utils: argument parsing, default simulation setup, recording context manager, trajectory replay, and window/user helpers.
• embodichain.lab.sim.demo_base.DemoBase: optional lifecycle base class for demos.

The existing scripts/tutorials/atomic_action/tutorial_utils.py now re-exports generic helpers while keeping UR5-specific configuration functions. All six atomic-action tutorials were migrated to DemoBase and the shared helpers; behavior is preserved.

Dependencies: None

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which improves an existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (existing functionality will not work without user modification)
• Documentation update

Checklist

• I have run the black . command to format the code base.
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• Dependencies have been updated, if applicable.