feat: Add Spring WebMVC streamable server transport provider

- Add WebMvcStreamableServerTransportProvider for non-reactive MCP server support
- Implement HTTP/SSE transport with session management and graceful shutdown
- Support GET, POST, DELETE endpoints for MCP protocol operations
- Add test suite including integration tests with Tomcat
- Refactor AbstractMcpAsyncServerTests to support multiple transport implementations
- Provide WebMVC alternative to existing WebFlux streamable transport

Related to #72

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

Author: tzolov