Ported splay-typed-octane.ts to RS

The most awkward addition I had to make: We have no way of expressing the invariant within a SplayTree that if this.root_ is non-null, it will still be non-null after calling this.splay_(), so I added a check after each such call which if it fails runs "throw new Error('This check should never fail');" The other (acceptably) intrusive changes I had to make are in splay_ and traverse_.

This PR also includes a copy of the python regression test, and partial work on the rest of octane.