[libc++][spaceship] Implement `operator<=>` for `duration`

Implements parts of [[ https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1614r2.html | P1614R2 ]]
Implemented `operator<=>` for `std::chrono::duration`

Reviewed By: #libc, Mordante

Differential Revision: https://reviews.llvm.org/D145881