feat(sandbox): add delegated access tokens

[BhautikChudasama]

Summary

• Add delegated sandbox token lifecycle methods and a separate token authenticated sandbox handle.
• Document the flow and bump the crate to 0.1.1. The default user agent follows the crate version.

Verification

• Cargo tests, formatting check, Clippy, and documentation generation passed before the version correction.
• Cargo package metadata now reports 0.1.1.