Fix pkg build checksum

[pata27]

Implement checksum verification for pkg build clone

• After cloning the git repo, if recipe.Checksum is provided, verify the HEAD commit hash matches
• Use 'git rev-parse HEAD' to get the commit hash
• Fail the build if checksum doesn't match to prevent using tampered code
• Remove TODO comment as checksum verification is now implemented

This ensures the cloned repository matches the expected commit for security.