Enhance leaderboard generation workflow and script permissions

[yunks128]

Purpose

• Improve the reliability and execution of the automated SLIM leaderboard generation process
• Fix script permissions and dependency installation issues

Proposed Changes

• [ADD] Make leaderboard.py script executable with chmod
• [ADD] Include leaderboard script directory in PATH
• [CHANGE] Update pip installation commands for better dependency management
• [CHANGE] Refine markdown status descriptions in leaderboard.py for better clarity
• [FIX] Streamline venv activation and dependency installation process

Testing

• Workflow changes have been tested through multiple iterations as evidenced by the commit history
• Changes validated through successful workflow runs on GitHub Actions

Notes

• These changes aim to resolve execution permission issues and improve the automation reliability
• Updates to the markdown formatting will provide clearer status descriptions in the generated leaderboards