perf: optimize advancing head and receding tail

[Wondertan]

Currently, we recede and advance the tail and head linearly, iterating and loading full headers. However, we can avoid doing so by simply checking header presence, similar to the Has method. The new algorithm would similarly iterate over header heights, but only checking their presence until it finds one that doesn't exist. Then it would simply return the highest known or lowest known ones for head and tail, respectively.