feat: Improve Tool schema handling

- Make McpSchema final and add private constructor
- Add JsonSchema record for structured schema representation
- Change Tool.inputSchema type from Map<String, Object> to JsonSchema.
- Use the String JSON Schema constructor when creating the Tool programaticaly.
- Enhance StdioClientTransport error logging with more context
- Add ToolHelper utility class for:
  - Converting Spring AI FunctionCallbacks to MCP tools
  - Generating JSON schemas for tool input validation
  - Facilitating integration between Spring AI functions and MCP tools
- Update tests and samples to use the new Tool schema format

Resolves #52

mcp/src/main/java/org/springframework/ai/mcp/client/transport/StdioClientTransport.java

@@ -275,14 +275,14 @@ public class StdioClientTransport implements ClientMcpTransport {
 						JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(this.objectMapper, line);
 						if (!this.inboundSink.tryEmitNext(message).isSuccess()) {
 							if (!isClosing) {
-								logger.error("Failed to enqueue inbound message");
+								logger.error("Failed to enqueue inbound message: {}", message);
 							}
 							break;
 						}
 					}
 					catch (Exception e) {
 						if (!isClosing) {
-							logger.error("Error processing inbound message", e);
+							logger.error("Error processing inbound message for line: " + line, e);
 						}
 						break;
 					}

mcp/src/main/java/org/springframework/ai/mcp/spec/McpSchema.java

@@ -38,7 +38,10 @@ import com.fasterxml.jackson.databind.ObjectMapper;
  *
  * @author Christian Tzolov
  */
-public class McpSchema {
+public final class McpSchema {
+
+	private McpSchema() {
+	}
 
 	public static final String LATEST_PROTOCOL_VERSION = "2024-11-05";
 
@@ -95,6 +98,8 @@ public class McpSchema {
 	// Sampling Methods
 	public static final String METHOD_SAMPLING_CREATE_MESSAGE = "sampling/createMessage";
 
+	private static ObjectMapper OBJECT_MAPPER = new ObjectMapper();
+
 	// ---------------------------
 	// JSON-RPC Error Codes
 	// ---------------------------
@@ -659,6 +664,15 @@ public class McpSchema {
 		@JsonProperty("nextCursor") String nextCursor) {
 	}// @formatter:on
 
+	@JsonInclude(JsonInclude.Include.NON_ABSENT)
+	@JsonIgnoreProperties(ignoreUnknown = true)
+	record JsonSchema( // @formatter:off
+		@JsonProperty("type") String type, 
+		@JsonProperty("properties") Map<String, Object> properties, 
+		@JsonProperty("required") List<String> required,
+		@JsonProperty("additionalProperties") Boolean additionalProperties) {
+	} // @formatter:on
+
 	/**
 	 * Represents a tool that the server provides. Tools enable servers to expose
 	 * executable functionality to the system. Through these tools, you can interact with
@@ -676,7 +690,7 @@ public class McpSchema {
 	public record Tool( // @formatter:off
 		@JsonProperty("name") String name,
 		@JsonProperty("description") String description,
-		@JsonProperty("inputSchema") Map<String, Object> inputSchema) {
+		@JsonProperty("inputSchema") JsonSchema inputSchema) {
 	
 		public Tool(String name, String description, String schema) {
 			this(name, description, parseSchema(schema));
@@ -684,9 +698,9 @@ public class McpSchema {
 			
 	} // @formatter:on
 
-	public static Map<String, Object> parseSchema(String schema) {
+	public static JsonSchema parseSchema(String schema) {
 		try {
-			return new ObjectMapper().readValue(schema, MAP_TYPE_REF);
+			return OBJECT_MAPPER.readValue(schema, JsonSchema.class);
 		}
 		catch (IOException e) {
 			throw new IllegalArgumentException("Invalid schema: " + schema, e);
@@ -724,6 +738,18 @@ public class McpSchema {
 	// ---------------------------
 	// Sampling Interfaces
 	// ---------------------------
+	@JsonInclude(JsonInclude.Include.NON_ABSENT)
+	public record ModelPreferences(// @formatter:off
+		@JsonProperty("hints") List<ModelHint> hints,
+		@JsonProperty("costPriority") Double costPriority,
+		@JsonProperty("speedPriority") Double speedPriority,
+		@JsonProperty("intelligencePriority") Double intelligencePriority) {
+	} // @formatter:on
+
+	@JsonInclude(JsonInclude.Include.NON_ABSENT)
+	public record ModelHint(@JsonProperty("name") String name) {
+	}
+
 	@JsonInclude(JsonInclude.Include.NON_ABSENT)
 	public record SamplingMessage(// @formatter:off
 		@JsonProperty("role") Role role,
@@ -803,18 +829,6 @@ public class McpSchema {
 		}
 	}// @formatter:on
 
-	// ---------------------------
-	// Model Preferences
-	// ---------------------------
-	@JsonInclude(JsonInclude.Include.NON_ABSENT)
-	public record ModelPreferences(List<ModelHint> hints, Double costPriority, Double speedPriority,
-			Double intelligencePriority) {
-	}
-
-	@JsonInclude(JsonInclude.Include.NON_ABSENT)
-	public record ModelHint(String name) {
-	}
-
 	// ---------------------------
 	// Pagination Interfaces
 	// ---------------------------