Rootkey Validator Tool

[hmmorales]

Adds a standalone CLI tool (rootkey_validator) that downloads a root key package from a URL and runs it through the full root key validation flow used by the Device Update agent. This tool enables engineers to quickly verify that a root key package can be downloaded, parsed, and validated against the hardcoded root keys without needing to deploy or run the full agent.

Validating root key packages currently requires running the full Device Update agent end-to-end. This tool provides a lightweight, targeted way to test the root key validation pipeline independently, which is useful for:

• Verifying new root key packages before rolling them out
• Debugging root key validation failures in isolation
• Testing with different download methods (curl vs. DeliveryOptimization)
• CI/CD validation of root key package integrity