Function create_worktree 

pub fn create_worktree(
    repo_root: &Path,
    worktree_path: &Path,
    branch: &str,
    base_branch: &str,
) -> Result<(), WorktreeError>

Creates a new worktree at worktree_path checked out on a newly created branch based on base_branch. Cleans up any partially created directory if git worktree add fails.