Refactors `startIter` to separate the traversal into two distinct passes: one for chain starts (nodes without left extension) and another specifically targeting cycle nodes. Also simplifies `nextUnitigKmer` by removing the redundant `_at_start_ parameter and unifying traversal direction logic. Updates `UnitigIter` to manage visited marking internally, improving encapsulation and cycle detection reliability.
Eric Coissac
0b784242cf