refactor: Rename 'data' to 'payload' in IPCMessage class for clarity

- Updated the IPCMessage class to replace the 'data' field with 'payload' for improved readability and consistency.
- Adjusted the constructor and getter method to reflect the new naming convention.
- Enhanced unit tests to verify the presence of 'payload' in the output, ensuring that the changes do not affect functionality.

Author: Marvin Zhang

src/main/java/io/crawlab/sdk/entity/IPCMessage.java

@@ -21,12 +21,12 @@ public String toString() {
     }
 
     private final String type;
-    private final Object data;
+    private final Object payload;
     protected final Boolean ipc = true;
 
-    public IPCMessage(MessageType type, Object data) {
+    public IPCMessage(MessageType type, Object payload) {
         this.type = type.toString().toLowerCase();
-        this.data = data;
+        this.payload = payload;
     }
 
     public String toJSON() {
@@ -42,8 +42,8 @@ public String getType() {
         return type;
     }
 
-    public Object getData() {
-        return data;
+    public Object getPayload() {
+        return payload;
     }
 
     public Boolean getIpc() {

src/test/java/io/crawlab/sdk/CrawlabSDKTest.java

@@ -24,6 +24,7 @@ void testSaveItemWithMap() {
         String output = outputStreamCaptor.toString().trim();
 
         assertTrue(output.contains("\"type\":\"data\""));
+        assertTrue(output.contains("\"payload\":["));
         assertTrue(output.contains("\"name\":\"John\""));
         assertTrue(output.contains("\"age\":25"));
         assertTrue(output.contains("\"ipc\":true"));
@@ -36,6 +37,7 @@ void testSaveItemWithClass() {
         String output = outputStreamCaptor.toString().trim();
 
         assertTrue(output.contains("\"type\":\"data\""));
+        assertTrue(output.contains("\"payload\":["));
         assertTrue(output.contains("\"name\":\"John\""));
         assertTrue(output.contains("\"age\":25"));
         assertTrue(output.contains("\"ipc\":true"));