DEV: allows stop/resume streaming on a message (#25774)

```ruby
ChatSDK::Message.start_stream(message_id: 1, guardian: guardian)
ChatSDK::Message.stream(raw: "foo", message_id: 1, guardian: guardian)
ChatSDK::Message.stream(raw: "bar", message_id: 1, guardian: guardian)
ChatSDK::Message.stop_stream(message_id: 1, guardian: guardian)
```

Generally speaking only admins or owners of the message can interact with a message.  Also note, Streaming to an existing message with a different user won't change the initial user of the message.

plugins/chat/lib/chat_sdk/message.rb

@@ -17,13 +17,13 @@ module ChatSDK
     # @yield [helper, message] Offers a block with a helper and the message for streaming operations.
     # @yieldparam helper [Helper] The helper object for streaming operations.
     # @yieldparam message [Message] The newly created message object.
-    # @return [ChMessage] The created message object.
+    # @return [Chat::Message] The created message object.
     #
     # @example Creating a simple message
     #   ChatSDK::Message.create(raw: "Hello, world!", channel_id: 1, guardian: Guardian.new)
     #
     # @example Creating a message with a block for streaming
-    #   Message.create_with_stream(raw: "Streaming message", channel_id: 1, guardian: Guardian.new) do |helper, message|
+    #   ChatSDK::Message.create_with_stream(raw: "Streaming message", channel_id: 1, guardian: Guardian.new) do |helper, message|
     #     helper.stream(raw: "Continuation of the message")
     #   end
     def self.create(**params, &block)
@@ -40,6 +40,70 @@ module ChatSDK
       self.create(**params, streaming: true, &block)
     end
 
+    # Streams to a specific chat message.
+    #
+    # @param raw [String] text to append to the existing message.
+    # @param message_id [Integer] the ID of the message to stream.
+    # @param guardian [Guardian] an instance of the guardian class, representing the user's permissions.
+    # @return [Chat::Message] The message object.
+    # @example Streaming a message
+    #   ChatSDK::Message.stream(message_id: 42, guardian: guardian, raw: "text")
+    def self.stream(raw:, message_id:, guardian:, &block)
+      new.stream(raw: raw, message_id: message_id, guardian: guardian, &block)
+    end
+
+    # Starts streaming for a specific chat message.
+    #
+    # @param message_id [Integer] the ID of the message for which streaming should be stopped.
+    # @param guardian [Guardian] an instance of the guardian class, representing the user's permissions.
+    # @return [Chat::Message] The message object.
+    # @example Starting the streaming of a message
+    #   ChatSDK::Message.start_stream(message_id: 42, guardian: guardian)
+    def self.start_stream(message_id:, guardian:)
+      new.start_stream(message_id: message_id, guardian: guardian)
+    end
+
+    # Stops streaming for a specific chat message.
+    #
+    # @param message_id [Integer] the ID of the message for which streaming should be stopped.
+    # @param guardian [Guardian] an instance of the guardian class, representing the user's permissions.
+    # @return [Chat::Message] The message object.
+    # @example Stopping the streaming of a message
+    #   ChatSDK::Message.stop_stream(message_id: 42, guardian: guardian)
+    def self.stop_stream(message_id:, guardian:)
+      new.stop_stream(message_id: message_id, guardian: guardian)
+    end
+
+    def start_stream(message_id:, guardian:)
+      message = Chat::Message.find(message_id)
+      guardian.ensure_can_edit_chat!(message)
+      message.update!(streaming: true)
+      ::Chat::Publisher.publish_edit!(message.chat_channel, message.reload)
+      message
+    end
+
+    def stream(message_id:, raw:, guardian:, &block)
+      message = Chat::Message.find(message_id)
+      helper = StreamHelper.new(message, guardian)
+      helper.stream(raw: raw)
+      ::Chat::Publisher.publish_edit!(message.chat_channel, message.reload)
+      message
+    end
+
+    def stop_stream(message_id:, guardian:)
+      with_service(Chat::StopMessageStreaming, message_id: message_id, guardian: guardian) do
+        on_success { result.message }
+        on_model_not_found(:message) { raise "Couldn't find message with id: `#{message_id}`" }
+        on_failed_policy(:can_join_channel) do
+          raise "User with id: `#{guardian.user.id}` can't join this channel"
+        end
+        on_failed_policy(:can_stop_streaming) do
+          raise "User with id: `#{guardian.user.id}` can't stop streaming this message"
+        end
+        on_failure { raise "Unexpected error" }
+      end
+    end
+
     def create(
       raw:,
       channel_id:,
@@ -75,14 +139,11 @@ module ChatSDK
           end
           on_failed_contract { |contract| raise contract.errors.full_messages.join(", ") }
           on_success { result.message_instance }
-          on_failure do
-            p Chat::StepsInspector.new(result)
-            raise "Unexpected error"
-          end
+          on_failure { raise "Unexpected error" }
         end
 
       if streaming && block_given?
-        helper = Helper.new(message)
+        helper = StreamHelper.new(message, guardian)
         block.call(helper, message)
       end
 
@@ -95,30 +156,28 @@ module ChatSDK
     end
   end
 
-  class Helper
+  class StreamHelper
     include Chat::WithServiceHelper
 
     attr_reader :message
+    attr_reader :guardian
 
-    def initialize(message)
-      @message = message
+    def initialize(message, guardian)
+      @message = message.reload
+      @guardian = guardian
     end
 
     def stream(raw: nil)
-      return false unless self.message.reload.streaming
+      return false if !self.message.streaming
+      return false if !raw
 
       with_service(
         Chat::UpdateMessage,
         message_id: self.message.id,
-        message: raw ? self.message.reload.message + " " + raw : self.message.message,
-        guardian: self.message.user.guardian,
+        message: self.message.message + raw,
+        guardian: self.guardian,
         streaming: true,
-      ) do
-        on_failure do
-          p Chat::StepsInspector.new(result)
-          raise "Unexpected error"
-        end
-      end
+      ) { on_failure { raise "Unexpected error" } }
 
       self.message
     end