Rax Integration

[BCathcart]

This PR replaces the rough custom RadixTree with Rax in our text index structure. RadixTree was naturally becoming more and more aligned with Rax, but without the space efficiency implemented yet. It makes more sense to switch to the well-used Rax and modify it as needed. Everything in this PR was done with some care except the PathIterator which I intend to redo with a follow-up in a week or so. Please ignore it. There are also opportunities for follow-up optimization:

• raxMutate uses the existing APIs to find the existing target and then update the target if needed with two traversals. It shouldn't be hard to only traverse once in every case.
• Use SIMD to compare outgoing edges to the search character while traversing (motivated by ART paper)
• Optimize the iterator. There were some lessons from implementing the RadixTree iterator I think we could use to get a small efficiency gain in the Rax iterator.