Allow supplying raw attachments/blocks for messages (#83)

* Allow supplying raw attachments
* Allow supplying blocks
* Format code with black

slackv3.py

@@ -748,6 +748,16 @@ def send_message(self, msg) -> Message:
                     "as_user": "true",
                 }
 
+                if index == len(parts) - 1:
+                    # Only add attachments/blocks if it's the last message, to avoid duplication
+                    if "attachments" in msg.extras:
+                        # If attachments are provided, and it's the last part of the mssage
+                        data["attachments"] = json.dumps(msg.extras["attachments"])
+
+                    if "blocks" in msg.extras:
+                        # If blocksare provided, and it's the last part of the mssage
+                        data["blocks"] = json.dumps(msg.extras["blocks"])
+
                 # Keep the thread_ts to answer to the same thread.
                 if "thread_ts" in msg.extras:
                     data["thread_ts"] = msg.extras["thread_ts"]