chore: use iwyu on graph/**.cpp

graph/kruskal.cpp

@@ -1,7 +1,10 @@
-#include <algorithm>
-#include <array>
-#include <iostream>
-#include <vector>
+#include <stdint.h>   // for int64_t
+#include <algorithm>  // for sort
+#include <array>      // for array
+#include <iostream>   // for char_traits, basic_istream::operator>>, basic_i...
+#include <vector>     // for vector
+#include <utility>    // for pair, make_pair
+
 //#include <boost/multiprecision/cpp_int.hpp>
 // using namespace boost::multiprecision;
 const int mx = 1e6 + 5;