feat!: add Streamable HTTP Client , multiple refactoring and improvements

[hashemix]

📌 Summary

The key feature added is Streamable HTTP support for MCP Clients (server-side support was previously released).
This PR also introduces significant updates that enhance SDK compliance, stability, and performance.

In addition, the architecture has been refined with changes that may be considered breaking. These adjustments could require minor updates to your existing code when upgrading.

🔍 Related Issues

• Streamable HTTP #62

✨ Changes Made

• Added ClientStreamableTransport, which integrates with HyperServer to enable StreamableHTTP transport. For backward compatibility, SSE transport can still be enabled via a flag in ServerOptions.
• Reorganized examples to better illustrate different scenarios and transport options.
• Refactored and regrouped error types for improved clarity and consistency.
• Added unit and integration tests to validate StreamableHTTP protocol compliance.
• Introduced a new SseParser to simplify and standardize stream parsing.