chore: onboard stepsecurity and apply security best practice

[ali-kafel]

This pull request updates the GitHub Actions workflow for the Foundry project to improve security and reliability. The main changes include hardening the runner, pinning action versions to specific commit hashes, and adjusting permissions.

Security improvements:

• Added the step-security/harden-runner action to block unwanted egress and enforce a global allowed endpoints policy, enhancing the security posture of the workflow.
• Set the id-token: write permission, preparing for potential use of OIDC authentication in the workflow.

Reliability and reproducibility:

• Updated all GitHub Actions (actions/checkout and foundry-rs/foundry-toolchain) to use pinned commit hashes instead of version tags, ensuring consistent and reproducible builds.