fix: add <cstdint> to ciphers/hill_cipher.cpp

ciphers/uint128_t.hpp

@@ -8,6 +8,7 @@
  */
 
 #include <algorithm>  /// for `std::reverse` and other operations
+#include <cstdint>    /// for integral typedefs
 #include <ostream>    /// for `std::cout` overload
 #include <string>     /// for `std::string`
 #include <utility>    /// for `std::pair` library