Add error handling tests for InMemoryTransport

[HoberMin]

This PR adds comprehensive error handling tests for the InMemoryTransport class, focusing on the onerror event handler implementation and test coverage.

Motivation and Context

The InMemoryTransport class had an onerror event handler defined but it wasn't being utilized in error scenarios. This change ensures proper error handling and notification when:

• Attempting to send messages without an established connection
• Sending messages after the connection is closed
• Both client and server sides of the connection

This improves the reliability and debugging capabilities of the transport layer.

How Has This Been Tested?

• Added new test cases in inMemory.test.ts
• Tested both client and server error scenarios
• Verified error handling in disconnected state
• Verified error handling after connection closure
• All tests pass successfully

Breaking Changes

No breaking changes. This is a non-breaking enhancement that adds error handling without modifying existing behavior.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

The changes focus on improving the robustness of the InMemoryTransport class by:

1. Adding proper error handling in the send method
2. Implementing comprehensive test coverage for error scenarios
3. Ensuring both client and server sides handle errors appropriately
4. Maintaining backward compatibility with existing code