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

pom.xml

@@ -66,7 +66,7 @@
 		<maven.compiler.source>17</maven.compiler.source>
 		<maven.compiler.target>17</maven.compiler.target>
 
-		<spring-ai.version>1.0.0-M4</spring-ai.version>
+		<spring-ai.version>1.0.0-M5</spring-ai.version>
 		<assert4j.version>3.26.3</assert4j.version>
 		<junit.version>5.10.2</junit.version>
 		<mockito.version>5.11.0</mockito.version>
@@ -100,9 +100,12 @@
 
 	<modules>
 		<module>mcp</module>
+		<module>mcp-transport/mcp-webflux-sse-transport</module>
+		<module>mcp-transport/mcp-webmvc-sse-transport</module>
 		<module>spring-ai-mcp</module>
-		<module>spring-ai-mcp-sample</module>
 		<module>mcp-docs</module>
+		<module>mcp-test</module>
+		<module>samples/spring-ai-mcp-sample</module>
 	</modules>
 
 	<build>