Allow version 0.19 of DataStructures

[LilithHafner]

• Allow version 0.19 of DataStructures
• Drop mostly-unnecessary test dep on StatsBase To be reverted. A simple hack to actually run tests.
• Revert "Drop mostly-unnecessary test dep on StatsBase"

[LilithHafner]

1.0 is still using DataStructures 0.18. lts, 1, and pre are using 0.19. This is because of DataStructures 0.19's julia compat

To verify that CI passes on the latest version of DataStructures, review the CI logs of 02df9a0.

[LilithHafner]

I've cross referenced the changelog of 0.19 with the source code of this package and found no incompatibilities. We do use heaps, but not the API that received breaking changes.