chore: copy plan marks when applying merge group

This became a necessity as we pretend to do early deployments at network
generation. In this scenario, when a "free" task context is merged into its
deployed counter part its plan marks is not carried out to the deployment task
instance. Then, this task instance would be garbage collected because it did
not carried the permanent mark from the replace "free" task context

lib/syskit/network_generation/merge_solver.rb

@@ -138,6 +138,7 @@ def apply_merge_group(merged_task_to_task)
 
                 merged_task_to_task.each do |merged_task, task|
                     unless merged_task.transaction_proxy?
+                        plan.copy_marks! from_task: merged_task, to_task: task
                         plan.remove_task(merged_task)
                     end
                     register_replacement(merged_task, task)

test/network_generation/test_merge_solver.rb

@@ -358,6 +358,31 @@ def mock_merged_task_with_concrete_input_connections(*connections)
         end
     end
 
+    describe "#apply_merge_group" do
+        attr_reader :local_plan, :solver
+        before do
+            @local_plan = Roby::Plan.new
+            @solver = Syskit::NetworkGeneration::MergeSolver.new(@local_plan)
+        end
+
+        # I don't like the "destination task" name but couldn't thought in a better one
+        it "applyes merged task plan marks to the destination task" do
+            task_1 = Roby::Task.new
+            task_2 = Roby::Task.new
+
+            local_plan.add_permanent_task task_1
+            local_plan.add_mission_task task_1
+
+            refute local_plan.permanent_task? task_2
+            refute local_plan.mission_task? task_2
+
+            solver.apply_merge_group({task_1 => task_2})
+
+            assert local_plan.permanent_task? task_2
+            assert local_plan.mission_task? task_2
+        end
+    end
+
     describe "functional tests" do
         describe "merging compositions" do
             attr_reader :plan, :srv_m, :task_m, :cmp_m