Use of std::iterator is deprecated

[mikee47]

This PR removes the use of std::iterator as it's deprecated in C++17.

[what-the-diff]

PR Summary

• Update iterator category
  Change the iterator_category to std::forward_iterator_tag for better compatibility
• Add type aliases
  Define iterator category, value type, difference type, and pointer/reference types using using statements
• Remove redundant template
  Remove an unnecessary template parameter from IteratorTemplate class definition