Add GCS bucket version audit and restore scripts

[anth-volk]

Summary

Add two Python scripts for auditing and restoring GCS bucket objects to a previous point-in-time using object versioning.

Scripts

gcs_version_audit.py (read-only)

• Lists all object versions in a GCS bucket
• Classifies each object: already correct, needs restore, or created after target date
• Reports total restore size and estimated Coldline retrieval cost
• Supports --limit for testing, --show-all-versions for verbose output, and --prefix for scoping

gcs_restore.py (write, with safeguards)

• Restores all objects to their state at a given target datetime
• Dry-run by default — requires --execute flag to make changes
• Even with --execute, prompts for interactive yes confirmation
• Parallel execution with configurable worker count
• Optional --delete-new flag to remove objects created after the target date

Use case

When a GCS bucket with object versioning enabled needs to be rolled back to a known-good state (e.g., after accidental bulk deletions or overwrites), these scripts provide a safe audit-then-restore workflow.

Requirements

• google-cloud-storage Python package
• GCP credentials with read access (audit) or read+write access (restore)
• Object versioning must be enabled on the target bucket