feat: Add HttpServlet streamable server transport provider

- Add HttpServletStreamableServerTransportProvider for MCP streamable transport
- Provides HttpServlet equivalent of WebMvcStreamableServerTransportProvider without Spring dependencies
- Support for GET (SSE connections/replay), POST (JSON-RPC messages), and DELETE (session cleanup) operations
- Include comprehensive integration test suite with sampling, elicitation, roots, and tools testing
- Add async/sync server test implementations for HttpServlet transport

Signed-off-by: Christian Tzolov <[email protected]>

Author: tzolov