Add Integration Tests for Exchange Simulator

[DieHard073055]

In order to ensure that our exchange simulator works correctly and handles various scenarios, we need to create a set of integration tests. These tests will cover the major functionalities of the simulator, such as creating a new instance, placing orders, and checking the wallet balance.

Tasks:

• Create a tests directory outside of the src directory for integration tests.
• Set up a testing framework, such as cargo test, for running integration tests.
• Write test cases that cover the following scenarios:
  • Creating a new exchange instance and verifying that the instance ID is returned.
  • Placing a limit buy order and checking that the order ID is returned.
  • Placing a limit sell order and checking that the order ID is returned.
  • Placing a market buy order and checking that the order ID is returned.
  • Placing a market sell order and checking that the order ID is returned.
  • Checking the wallet balance after placing orders and verifying the balance is updated correctly.
  • Checking the wallet transactions after placing orders and verifying the transactions are