Pin GitHub Actions to commit hashes

This pull request pins all GitHub Actions in workflow files to specific commit hashes to improve security and ensure reproducible builds.

Changes Made

• Converted version tags (e.g., v3, v4) to commit hashes
• Added comments showing the original version and date for reference
• Preserved all existing functionality while improving security

Benefits

• Security: Prevents supply chain attacks by ensuring immutable action references
• Reproducibility: Guarantees the same action version is used across all runs
• Auditability: Clear tracking of which specific version of each action is being used

Review Notes

• All pinned actions maintain their original functionality
• Comments preserve the original version information with dates for easy reference
• No workflow behavior changes are expected

This change follows GitHub's security best practices for action pinning.