* 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
* Re-route KeyError exceptions as Defect for all except the `[]` function
why:
Access via key is verified, error is returned via Result[]
* Refactor lruFetch() item rotation
why:
Previously, the item was deleted and re-inserted in the table although
for rotation, only the queue links need to be updated.
* Delete some KeyError annotations
why:
Was overlooked earlier
* More KeyError fixes
