Clear object names list on initialization

[tkgaolol]

Description

This PR fixes a bug in RigidObjectCollection where _object_names_list accumulates duplicate entries when the simulation resets multiple times, leading to incorrect object counts.

Fixes # (4258)

Problem:
When using workflows that trigger multiple simulation resets (e.g., record_demos.py), the _initialize_impl() method gets called multiple times without clearing the existing _object_names_list, causing duplicate object names to be appended.

Solution:
Added self._object_names_list.clear() at the beginning of _initialize_impl() to ensure the list is reset before repopulating it, making the initialization process idempotent.

Test Command:

python scripts/tools/record_demos.py --task Isaac-Stack-Cube-Instance-Randomize-Franka-IK-Rel-v0 --teleop_device keyboard

Type of change

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

Screenshots

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there