chore: use iwyu on graph/**.cpp

graph/connected_components.cpp

@@ -25,10 +25,9 @@
  *
  */
 
-#include <algorithm>
-#include <cassert>
-#include <iostream>
-#include <vector>
+#include <cassert>   // for assert
+#include <iostream>  // for basic_ostream, char_traits, operator<<, basic_is...
+#include <vector>    // for vector
 
 /**
  * @namespace graph