Multiple fixes: signed/unsigned, etc... (#600)

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/dom/flexbox_test.cpp

@@ -6,6 +6,7 @@
 #include "ftxui/dom/node.hpp"            // for Render
 #include "ftxui/screen/screen.hpp"       // for Screen
 
+// NOLINTBEGIN
 namespace ftxui {
 
 TEST(FlexboxTest, BasicRow) {
@@ -454,6 +455,7 @@ TEST(FlexboxTest, Focus) {
 }
 
 }  // namespace ftxui
+// NOLINTEND
 
 // Copyright 2021 Arthur Sonzogni. All rights reserved.
 // Use of this source code is governed by the MIT license that can be found in