feat(mcp): Add builder for CreateMessageRequest

- Implements a builder pattern for CreateMessageRequest
- Updates corresponding tests to use the new builder syntax

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -799,6 +799,66 @@ public enum ContextInclusionStrategy {
 			@JsonProperty("thisServer") THIS_SERVER,
 			@JsonProperty("allServers") ALL_SERVERS
 		}
+		
+		public static Builder builder() {
+			return new Builder();
+		}
+
+		public static class Builder {
+			private List<SamplingMessage> messages;
+			private ModelPreferences modelPreferences;
+			private String systemPrompt;
+			private ContextInclusionStrategy includeContext;
+			private Double temperature;
+			private int maxTokens;
+			private List<String> stopSequences;
+			private Map<String, Object> metadata;
+
+			public Builder messages(List<SamplingMessage> messages) {
+				this.messages = messages;
+				return this;
+			}
+
+			public Builder modelPreferences(ModelPreferences modelPreferences) {
+				this.modelPreferences = modelPreferences;
+				return this;
+			}
+
+			public Builder systemPrompt(String systemPrompt) {
+				this.systemPrompt = systemPrompt;
+				return this;
+			}
+
+			public Builder includeContext(ContextInclusionStrategy includeContext) {
+				this.includeContext = includeContext;
+				return this;
+			}
+
+			public Builder temperature(Double temperature) {
+				this.temperature = temperature;
+				return this;
+			}
+
+			public Builder maxTokens(int maxTokens) {
+				this.maxTokens = maxTokens;
+				return this;
+			}
+
+			public Builder stopSequences(List<String> stopSequences) {
+				this.stopSequences = stopSequences;
+				return this;
+			}
+
+			public Builder metadata(Map<String, Object> metadata) {
+				this.metadata = metadata;
+				return this;
+			}
+
+			public CreateMessageRequest build() {
+				return new CreateMessageRequest(messages, modelPreferences, systemPrompt, 
+					includeContext, temperature, maxTokens, stopSequences, metadata);
+			}
+		}
 	}// @formatter:on
 
 	@JsonInclude(JsonInclude.Include.NON_ABSENT)

mcp/src/test/java/io/modelcontextprotocol/spec/McpSchemaTests.java

@@ -524,10 +524,16 @@ void testCreateMessageRequest() throws Exception {
 		Map<String, Object> metadata = new HashMap<>();
 		metadata.put("session", "test-session");
 
-		McpSchema.CreateMessageRequest request = new McpSchema.CreateMessageRequest(Collections.singletonList(message),
-				preferences, "You are a helpful assistant",
-				McpSchema.CreateMessageRequest.ContextInclusionStrategy.THIS_SERVER, 0.7, 1000,
-				Arrays.asList("STOP", "END"), metadata);
+		McpSchema.CreateMessageRequest request = McpSchema.CreateMessageRequest.builder()
+			.messages(Collections.singletonList(message))
+			.modelPreferences(preferences)
+			.systemPrompt("You are a helpful assistant")
+			.includeContext(McpSchema.CreateMessageRequest.ContextInclusionStrategy.THIS_SERVER)
+			.temperature(0.7)
+			.maxTokens(1000)
+			.stopSequences(Arrays.asList("STOP", "END"))
+			.metadata(metadata)
+			.build();
 
 		String value = mapper.writeValueAsString(request);
 
@@ -543,8 +549,12 @@ void testCreateMessageRequest() throws Exception {
 	void testCreateMessageResult() throws Exception {
 		McpSchema.TextContent content = new McpSchema.TextContent("Assistant response");
 
-		McpSchema.CreateMessageResult result = new McpSchema.CreateMessageResult(McpSchema.Role.ASSISTANT, content,
-				"gpt-4", McpSchema.CreateMessageResult.StopReason.END_TURN);
+		McpSchema.CreateMessageResult result = McpSchema.CreateMessageResult.builder()
+			.role(McpSchema.Role.ASSISTANT)
+			.content(content)
+			.model("gpt-4")
+			.stopReason(McpSchema.CreateMessageResult.StopReason.END_TURN)
+			.build();
 
 		String value = mapper.writeValueAsString(result);