message: [admission-control] Add service test into lib
  Closes:
  Approved by: phlip9
diff: //! 1. SubmitTransaction, to submit transaction to associated validator.
  //! 2. UpdateToLatestLedger, to query storage, e.g. account state, transaction log, and proofs.
  +#[cfg(test)]
  +#[path = "unit_tests/admission_control_service_test.rs"]
  +mod admission_control_service_test;
  +
  #[cfg(feature = "fuzzing")]
  /// Fuzzer for admission control
  pub mod admission_control_fuzzing;
  