SseClientTransport 404 error

[gqf2008]

Describe the bug
SSE client transport fails with 404 Not Found error when trying to connect to the SSE endpoint.

To Reproduce
Steps to reproduce the behavior:

1. Run the client with SseClientTransport::start("http://127.0.0.1:8003/sse").await?;
2. Observe the 404 error when attempting to send the initialize request

Expected behavior
The client should successfully establish an SSE connection with the server at the specified endpoint.

Logs
2025-05-19T02:48:33.531669Z ERROR test_client: Client error: Send message error Client error: HTTP status client error (404 Not Found) for url (http://127.0.0.1:8003/sse/message?sessionId=ddd789ed-dae2-46bf-bbb8-f5c917840b52), when send initialize request

Additional context

• The error occurs during the initialization phase
• The server might not have the correct SSE endpoint implemented
• Verify the server is running and the endpoint URL is correct

[4t145]

I knew, I will fix this in #197