Function lock_key 

pub fn lock_key(entry: &Entry) -> String

Generate the lock file key for an entry: "{source_type}/{entity_type}/{name}".

use skillfile_core::models::*;
use skillfile_core::lock::lock_key;

let entry = Entry {
    entity_type: EntityType::Agent,
    name: "code-refactorer".into(),
    source: SourceFields::Github {
        owner_repo: "owner/repo".into(),
        path_in_repo: "agents/code-refactorer.md".into(),
        ref_: "main".into(),
    },
};
assert_eq!(lock_key(&entry), "github/agent/code-refactorer");