set loggingConsumer after client initialization

Expected Behavior

We should be able to set a loggingConsumer on McpClient after querying its capabilities.

var capabilities = client.getServerCapabilities();
if (capabilities.logging() != null) {
    client.setLoggingLevel(McpSchema.LoggingLevel.INFO);
    client.setLoggingConsumer(consumer);
}

Current Behavior

Currently, we can set a loggingConsumer with McpClientTransport before client initialization. For example,

McpClient.sync(server.transport())
                .loggingConsumer(consumer)
                .build();

Context

However, many MCP servers' logging capabilities are not enabled. But we cannot query if the server has this capability before client initialization. Such a poor design makes it impossible to register a logging consumer safely.

首先阅读 McpClient 的初始化和能力查询流程，然后将其与 McpClientTransport 的 loggingConsumer 配置进行比较。验证 setLoggingLevel 和 setLoggingConsumer 在初始化之前的行为。完成标准是：在 getServerCapabilities() 确认支持 logging 后，可以注册一个 consumer，同时不破坏现有的初始化前 builder 用法。