user: add is_internal_user? helper function

lib/pleroma/user.ex

@@ -1410,4 +1410,8 @@ defp put_password_hash(
   end
 
   defp put_password_hash(changeset), do: changeset
+
+  def is_internal_user?(%User{nickname: nil}), do: true
+  def is_internal_user?(%User{local: true, nickname: "internal." <> _}), do: true
+  def is_internal_user?(_), do: false
 end

test/user_test.exs

@@ -1310,4 +1310,21 @@ test "without args", %{user: user} do
       assert following == 0
     end
   end
+
+  describe "is_internal_user?/1" do
+    test "non-internal user returns false" do
+      user = insert(:user)
+      refute User.is_internal_user?(user)
+    end
+
+    test "user with no nickname returns true" do
+      user = insert(:user, %{nickname: nil})
+      assert User.is_internal_user?(user)
+    end
+
+    test "user with internal-prefixed nickname returns true" do
+      user = insert(:user, %{nickname: "internal.test"})
+      assert User.is_internal_user?(user)
+    end
+  end
 end