message: [pdsl_model] Simplify imports for pdsl_model test
diff: -use crate::{
  - contract::{ContractDecl, ContractInstance, Contract},
  - state::ContractState,
  - msg::Message,
  -};
  -use pdsl_core::{
  - storage::{self, alloc::Initialize},
  -};
  +use crate::contract::{ContractDecl, Contract};
  +use pdsl_core::storage;
  state! {
  /// A simple contract having just one value that can be incremented and returned.
  