Move pack test from crypto3::detail to this module

[nkaskov]

At the moment, pack algorithm is part of long-running backlog. It is placed in the crypto3::detail namespace. We must substitute it by the marshalling pack. To be sure, that we made correct substitution, we need to move pack tests to marshalling and ensure, that there is no probplems with that.

[nkaskov]

All pack old tests for big-endian and little-endian work. little-endian and big-endian tests are to be finished after closing #8