Add Comprehensive Test Suite

[bobbyiliev]

Expand the test suite to cover more of the codebase and protocol implementation.

Description:
Current test coverage is limited. Adding comprehensive tests will help ensure the mock server behaves correctly.

Tasks:

• Add unit tests for all protocol message builders
• Add unit tests for all protocol message processors
• Add integration tests for full message flows
• Add connection lifecycle tests
• Add edge case and error handling tests
• Set up CI to run tests and report coverage

Related files:

• tests/ directory
• jest.config.js