fix: Made range arrayFormat overload more elegant + minor fixes

[eric-bodhi]

Running on latest GCC version and ubuntu 22.04 I was getting conversion warnings from arrayFormat(start, end) overload specifically when used with sortedSizeArrayElement in word_test.cpp

Primary Warnings thrown:
In instantiation of function template specialization 'faker::word::sortedSizeArrayElement<__gnu_cxx::__normal_iterator<std::basic_string *, std::vector<std::basic_string>>>' /home/eric/github/faker-cxx/include/faker-cxx/helper.h:64:18: warning: implicit conversion changes signedness: 'unsigned long const' to '__gnu_cxx::__normal_iterator<std::basic_string *, std::vector<std::basic_string>>::difference_type' (aka 'long')

Fixed arrayFormat to enforce input_iterator concept in templates and fixed implicit conversion in index return of the function.
Cleaned up boolean(probability) of datatype.cpp

• Originally checked ifnan through if (probability != nan("")) now uses std::isnan function