refactor: Split transport implementations into modules

Split the  transport implementations into dedicated modules to improve modularity
and reduce core dependencies.

Added shared test module for common test utilities.

Key changes:

- Create mcp-transport/mcp-webflux-sse-transport module
 - Move SseClientTransport → WebFluxSseClientTransport
 - Move SseServerTransport → WebFluxSseServerTransport
 - Move related tests and utilities

- Create mcp-transport/mcp-webmvc-sse-transport module
 - Add new WebMvcSseServerTransport implementation
 - Add corresponding tests and integration tests

- Add framework-independent SSE client implementations to core module
 - Add FlowSseClient using java.net.http
 - Add HttpClientSseClientTransport using java.net.http

- Keep StdioClientTransport/StdioServerTransport in core (no external deps)

- Create mcp-test module for shared test infrastructure
 - Move abstract test base classes
 - Move shared test utilities and mocks
 - Update test dependencies

The modular approach allows users to choose between:

- Framework-specific implementations (WebFlux/WebMVC)
- Pure Java implementations (java.net.http)
- Basic implementations (STDIO)

Add breaking changes readme: 0.5.0-BREAKING-CHANGES.md

Resolves #54

spring-ai-mcp/pom.xml

@@ -24,12 +24,29 @@
 			<groupId>org.springframework.ai</groupId>
 			<artifactId>spring-ai-core</artifactId>
 			<version>${spring-ai.version}</version>
+			<exclusions>
+				<exclusion>
+					<groupId>org.springframework</groupId>
+					<artifactId>spring-context</artifactId>
+				</exclusion>
+				<exclusion>
+					<groupId>org.springframework</groupId>
+					<artifactId>spring-messaging</artifactId>
+				</exclusion>
+			</exclusions>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.experimental</groupId>
 			<artifactId>mcp</artifactId>
 			<version>${project.version}</version>
 		</dependency>
+
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-core</artifactId>
+			<version>${springframework.version}</version>
+		</dependency>
+
 	</dependencies>
 
 </project>