RangeTombstonListTest sometimes fails on trunk

I've seen random failures with RangeTombstoneList.addAllRandomTest. The problem is 2 inequalities in RangeTombstoneList.insertFrom that should be inclusive rather than strict when we deal with boundaries between range. In practice, that makes us consider range like [3, 3) during addition, which is non-sensical.

Attaching patch as well as a test that reproduce (extracted from addAllRandomTest with a failing seed).