Modify the len method to be constant-time#105

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Kerollmops wants to merge 6 commits intomainfrom constant-time-len

+540-63

Commits on Apr 30, 2021

Improve the ref-ref RoaringBitmap union
Kerollmops
committed

Commits on May 2, 2021

Implement a constant-time len method
Kerollmops
committed