feat(headers): add SDK tracking headers to all DashScope requests

Every outbound DashScope request now carries three new headers:

- x-dashscope-sdk-client: identifies the SDK ("java-sdk")
- x-dashscope-sdk-version: current SDK version (from Version.version)
- x-dashscope-sdk-session-id: a process-level UUID, generated once at
  class load and reused for the lifetime of the JVM

These headers are set before user-supplied customHeaders are merged, so
callers can override any of them if needed. Setting the environment
variable DASHSCOPE_DISABLE_SDK_HEADERS=1 (or true) opts out entirely.

Both HTTP (buildHttpHeaders) and WebSocket (buildWebSocketHeaders)
paths are covered, so all API calls — including Generation,
MultiModalConversation, image/video synthesis, TTS, etc. — will
automatically include the tracking metadata.

Author: luk384090-cloud

src/main/java/com/alibaba/dashscope/protocol/DashScopeHeaders.java

@@ -33,17 +33,15 @@ public static String userAgent(String customUserAgent) {
     return userAgent;
   }
 
-  /**
-   * Check if SDK tracking headers are disabled via DASHSCOPE_DISABLE_SDK_HEADERS env var.
-   */
+  /** Check if SDK tracking headers are disabled via DASHSCOPE_DISABLE_SDK_HEADERS env var. */
   private static boolean isSdkHeadersDisabled() {
     String disable = System.getenv("DASHSCOPE_DISABLE_SDK_HEADERS");
     return "1".equals(disable) || "true".equalsIgnoreCase(disable);
   }
 
   /**
-   * Add SDK tracking headers to the given map.
-   * These headers are set first so that user-supplied customHeaders can override them.
+   * Add SDK tracking headers to the given map. These headers are set first so that user-supplied
+   * customHeaders can override them.
    */
   private static void addSdkTrackingHeaders(Map<String, String> headers) {
     if (!isSdkHeadersDisabled()) {