chore: try to comply to C++20 (#2978)

* chroe: add cstdint

* fix: remove <> from explicit function

machine_learning/a_star_search.cpp

@@ -22,12 +22,14 @@
 #include <algorithm>   /// for `std::reverse` function
 #include <array>       /// for `std::array`, representing `EightPuzzle` board
 #include <cassert>     /// for `assert`
+#include <cstdint>     /// for `std::uint32_t`
 #include <functional>  /// for `std::function` STL
 #include <iostream>    /// for IO operations
 #include <map>         /// for `std::map` STL
 #include <memory>      /// for `std::shared_ptr`
 #include <set>         /// for `std::set` STL
 #include <vector>      /// for `std::vector` STL
+
 /**
  * @namespace machine_learning
  * @brief Machine learning algorithms