* Add support for subsecond printing for std::chrono::duration according to the c++20 standard

* Remove assert test that overflows intmax_t

* * Hopefully fix int64_t to int32_t conversion errors.
* Allow proper Duration::rep type to propagate via template argument deduction

* * Hopefully fix int64_t to int32_t conversion errors.
* Allow proper Duration::rep type to propagate via template argument deduction

* Fix sign conversion (-Wsign-conversion) warning treated as error in num_digits()

* Format chrono.h with clang-format

* Remove extra forward slash in doxygen style comment
Co-authored-by: Victor Zverovich <victor.zverovich@gmail.com>

* Apply all suggestions from GitHub, except for replacing the utility subsecond_helper class with a function

* * Move logic of handling subseconds from utility class to function with name write_fractional_seconds()
* Revert write(Rep value, int width) function to previous state

* Fix -Wshadow warning

* Remove unsued get_subseconds() function, its logic has been moved to write_fractional_seconds()

* Change comment from lowercase int to uppercase Int

* Simplify test check

* Integrate suggested changes

* Remove static from detail functions, they are no longer member functions of a class and static is unnecessary.
* Change comment from "amount" to "number"
Co-authored-by: Victor Zverovich <victor.zverovich@gmail.com>