* Migrate to `unittest2`
why:
Global symbol overflow when running NIM 1.2 on Github ci suggests that
unit tests run sort of separately. The replacement library `unittest2`
provides that.
* Build ci dependencies
* Added `IntervalSet`, sets of non-adjacent intervals
Relocated from nimbus-eth1 snap sync development
* Fix local import directive
* Fix --styleCheck complaints
* Attempt to get around CI problem by varying items
details:
Vary all_tests exec list
Hide useless globalness of `noisy` constant in non-debugging mode
Jordan Hrycaj
tersec