Remove &mut self from StateReader.

[marioiordanov]

In state::state_api::StateReader all methods of the interface require a &mut self. In starknet-devnet-rs when using some method of StateReader we have to pass &mut reference which in some cases result in compilation errors like: cannot borrow as mutable more than once at a time or cannot borrow *self as immutable because it is also borrowed as mutable