BTree: move more shared iterator code into navigate.rs The functions in navigate.rs only exist to support iterators, and these look easier on my eyes if there is a shared `struct` with the recurring pair of handles. r? `@Mark-Simulacrum`
BTree: move more shared iterator code into navigate.rs The functions in navigate.rs only exist to support iterators, and these look easier on my eyes if there is a shared `struct` with the recurring pair of handles. r? `@Mark-Simulacrum`