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

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

src/ftxui/dom/gridbox_test.cpp

@@ -1,6 +1,6 @@
 #include <gtest/gtest.h>
-#include <stddef.h>   // for size_t
 #include <algorithm>  // for remove
+#include <cstddef>    // for size_t
 #include <memory>     // for shared_ptr
 #include <string>     // for allocator, basic_string, string
 #include <vector>     // for vector
@@ -9,6 +9,7 @@
 #include "ftxui/dom/node.hpp"      // for Render
 #include "ftxui/screen/screen.hpp"  // for Screen
 
+// NOLINTBEGIN
 namespace ftxui {
 
 namespace {
@@ -615,6 +616,7 @@ TEST(GridboxTest, Focus) {
 }
 
 }  // namespace ftxui
+// NOLINTEND
 
 // Copyright 2020 Arthur Sonzogni. All rights reserved.
 // Use of this source code is governed by the MIT license that can be found in