Fix tr_unique algorithm

[emricksinisonos]

⚠️ As this is a bug still present in OpenFST, I have commented a test that fails because of the update. It is required to find a way to fix OpenFST in order to make this test pass.

// TODO: Fix openFST to run this test
//#[test]
//fn test_state_map_tr_unique_openfst() -> Result<()> {
//    do_run!(test_state_map_tr_unique, $fst_name);
//    Ok(())
//}