Implement efficient seeking from non-null trees using tree_pos#2911

Draft

duncanMR wants to merge 2 commits intotskit-dev:mainfrom duncanMR:seek_revision

+145-8

Commits on Feb 26, 2024

Add tree seek_forward and seek_backward and revise seek linear
duncanMR
committed

Commits on Mar 5, 2024

Restore seek_linear and add seek_skip as an option
duncanMR
committed