test(server): add more tests for SSEServerTransport class

[christian-bromann]

Motivation and Context

I've been skimming through the code and discovered that there is an opportunity to add more tests to the SSEServerTransport class. That's it!

Note: the package-lock.json change is not intended but it seems to be missing the recent update. Happy to revert though.

How Has This Been Tested?

I added unit tests.

Breaking Changes

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

[ihrpr]

Thank you for improving SDK. Sorry about the delay in PR reviews. Those files have conflicts now, please can you merge main and please revert package-lock changes

[ihrpr]

Thank you

[ihrpr]

oh, looks like test "should return 202 if message has a valid schema" is failing in CI

[ihrpr]

🙏