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

0.5.0-BREAKING-CHANGES.md

@@ -0,0 +1,105 @@
+# Breaking Changes for Spring AI MCP 0.5.0-SNAPSHOT
+
+## Major Changes
+
+1. Transport Implementation Modularization
+   - SSE transport implementations have been moved to dedicated modules:
+     - `mcp-webflux-sse-transport`: WebFlux-based SSE transport
+     - `mcp-webmvc-sse-transport`: WebMVC-based SSE transport
+   - Base MCP module no longer includes transport implementations
+
+2. Class Renames
+   - `SseClientTransport` → `WebFluxSseClientTransport`
+   - `SseServerTransport` → `WebFluxSseServerTransport`
+
+3. Project Structure
+   - Test utilities moved to new `mcp-test` module
+   - Sample application moved to `samples/` directory
+
+## Migration Guide
+
+### 1. Update Dependencies
+
+If using SSE transport, add the appropriate transport module to your pom.xml:
+
+For WebFlux SSE transport:
+```xml
+<dependency>
+    <groupId>org.springframework.experimental</groupId>
+    <artifactId>mcp-webflux-sse-transport</artifactId>
+    <version>0.5.0-SNAPSHOT</version>
+</dependency>
+```
+
+For WebMVC SSE transport:
+```xml
+<dependency>
+    <groupId>org.springframework.experimental</groupId>
+    <artifactId>mcp-webmvc-sse-transport</artifactId>
+    <version>0.5.0-SNAPSHOT</version>
+</dependency>
+```
+
+### 2. Update Transport Class References
+
+Replace:
+```java
+import org.springframework.ai.mcp.client.transport.SseClientTransport;
+import org.springframework.ai.mcp.server.transport.SseServerTransport;
+```
+
+With:
+```java
+// For WebFlux
+import org.springframework.ai.mcp.client.transport.WebFluxSseClientTransport;
+import org.springframework.ai.mcp.server.transport.WebFluxSseServerTransport;
+
+// Or for WebMVC
+import org.springframework.ai.mcp.server.transport.WebMvcSseServerTransport;
+```
+
+### 3. Update Transport Instantiation
+
+Replace:
+```java
+var transport = new SseClientTransport(webClientBuilder);
+```
+
+With:
+```java
+var transport = new WebFluxSseClientTransport(webClientBuilder);
+```
+
+Replace:
+```java
+var serverTransport = new SseServerTransport(objectMapper, messageEndpoint);
+```
+
+With:
+```java
+// For WebFlux
+var serverTransport = new WebFluxSseServerTransport(objectMapper, messageEndpoint);
+
+// Or for WebMVC
+var serverTransport = new WebMvcSseServerTransport(objectMapper, messageEndpoint);
+```
+
+### 4. Test Dependencies
+
+If you're using MCP test utilities, add the test module dependency:
+
+```xml
+<dependency>
+    <groupId>org.springframework.experimental</groupId>
+    <artifactId>mcp-test</artifactId>
+    <version>0.5.0-SNAPSHOT</version>
+    <scope>test</scope>
+</dependency>
+```
+
+## Other Changes
+
+- Spring AI dependency updated to 1.0.0-M5
+- Improved dependency management and reduced transitive dependencies
+- Sample application restructured under samples/ directory
+- New test utilities and base test classes in mcp-test module