GH-3403: Add caching for JSON schema generation in function calling

[Seol-JY]

Fixes GH-3403

Add ConcurrentHashMap-based caching to eliminate repeated schema generation for identical method signatures in tool invocations.

• Cache tool definitions by Method instance in ToolDefinitions
• Cache JSON schemas with method signature + options as key
• Add comprehensive test coverage for caching behavior

Performance improvement: Eliminates CPU overhead from repeated schema generation in function calling applications.

[YunKuiLu]

Can we also cache ToolCallback[] in MethodToolCallbackProvider ? 🤔

Such as:

public final class MethodToolCallbackProvider implements ToolCallbackProvider {
    @Override
    public ToolCallback[] getToolCallbacks() {
    if (this.cachedToolCallbacks == null) {
	    synchronized (this) {
		    if (this.cachedToolCallbacks == null) {
			    var toolCallbacks = this.toolObjects.stream()
				    .map(toolObject -> Stream
					    .of(ReflectionUtils.getDeclaredMethods(AopUtils.isAopProxy(toolObject)
							    ? AopUtils.getTargetClass(toolObject) : toolObject.getClass()))
					    .filter(this::isToolAnnotatedMethod)
					    .filter(toolMethod -> !isFunctionalType(toolMethod))
					    .filter(ReflectionUtils.USER_DECLARED_METHODS::matches)
					    .map(toolMethod -> MethodToolCallback.builder()
						    .toolDefinition(ToolDefinitions.from(toolMethod))
						    .toolMetadata(ToolMetadata.from(toolMethod))
						    .toolMethod(toolMethod)
						    .toolObject(toolObject)
						    .toolCallResultConverter(ToolUtils.getToolCallResultConverter(toolMethod))
						    .build())
					    .toArray(ToolCallback[]::new))
				    .flatMap(Stream::of)
				    .toArray(ToolCallback[]::new);
    
			    validateToolCallbacks(toolCallbacks);
    
			    this.cachedToolCallbacks = toolCallbacks;
		    }
	    }
    }
    return this.cachedToolCallbacks;
    }
}