Refactor: Cycles: Automated clang-tidy fixups in Cycles

* Use .empty() and .data()
* Use nullptr instead of 0
* No else after return
* Simple class member initialization
* Add override for virtual methods
* Include C++ instead of C headers
* Remove some unused includes
* Use default constructors
* Always use braces
* Consistent names in definition and declaration
* Change typedef to using

Pull Request: https://projects.blender.org/blender/blender/pulls/132361

tests/gtests/testing/testing.h

@@ -6,9 +6,9 @@
 
 #include <vector>
 
-#include "gflags/gflags.h"
-#include "glog/logging.h"
-#include "gtest/gtest.h"
+#include <gflags/gflags.h>  // IWYU pragma: export
+#include <glog/logging.h>   // IWYU pragma: export
+#include <gtest/gtest.h>    // IWYU pragma: export
 
 namespace blender::tests {