fix: resolve duplicate requests caused by concurrent message sending

[JooKS-me]

Motivation and Context

When calling the tools/call method of the same mcp async-client in parallel, we found that the client occasionally sent duplicate messages. We located that the same requestBuilder was used each time a request was made in the SDK, which was thread-unsafe.

How Has This Been Tested?

        ExecutorService threadPool = Executors.newFixedThreadPool(5);

        var transport = HttpClientSseClientTransport.builder("xxxxxx")
                .sseEndpoint("xxxxxx")
                .build();
        var asyncClient = McpClient.async(transport).build();

        asyncClient.initialize().block(Duration.ofSeconds(10));
        Map<String, Object> arguments = new HashMap<>();
        McpSchema.CallToolRequest request = new McpSchema.CallToolRequest("xxxxxx", arguments);

        Mono<McpSchema.CallToolResult> mono1 = asyncClient.callTool(request)
                .timeout(Duration.ofSeconds(30))
                .doOnSuccess(result -> {
                    System.out.println("--> get success response" + result);
                })
                .doOnError(error -> {
                    System.out.println("failed");
                    System.out.println(error.getMessage());
                });

        Mono<McpSchema.CallToolResult> mono2 = asyncClient.callTool(request)
                .timeout(Duration.ofSeconds(30))
                .doOnSuccess(result -> {
                    System.out.println("--> get success response" + result);
                })
                .doOnError(error -> {
                    System.out.println("failed");
                    System.out.println(error.getMessage());
                });

        Mono<McpSchema.CallToolResult> mono3 = asyncClient.callTool(request)
                .timeout(Duration.ofSeconds(30))
                .doOnSuccess(result -> {
                    System.out.println("--> get success response" + result);
                })
                .doOnError(error -> {
                    System.out.println("failed");
                    System.out.println(error.getMessage());
                });

        Mono<McpSchema.CallToolResult> mono4 = asyncClient.callTool(request)
                .timeout(Duration.ofSeconds(30))
                .doOnSuccess(result -> {
                    System.out.println("--> get success response" + result);
                })
                .doOnError(error -> {
                    System.out.println("failed");
                    System.out.println(error.getMessage());
                });

        Thread.sleep(10000);

        threadPool.submit(() -> {
            mono1.subscribe();
        });

        threadPool.submit(() -> {
            mono2.subscribe();
        });

        threadPool.submit(() -> {
            mono3.subscribe();
        });

        threadPool.submit(() -> {
            mono4.subscribe();
        });

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[tzolov]

Nice catch @JooKS-me , thank you.
Can you please run ./mvnw spring-javaformat:apply to resolve the formatting issues.

[JooKS-me]

Nice catch @JooKS-me , thank you. Can you please run ./mvnw spring-javaformat:apply to resolve the formatting issues.

OK，it's done~

[tzolov]

Thank you @JooKS-me

Rebased, squashed and merged at fce7a6b