Mark Many As Read Tracking Scaling

Faster read-file tracking with the mark-many-as-read experiment

With the mark-many-as-read experiment enabled, Terragrunt records every module file it marks as read during parsing. The bookkeeping for that record scaled quadratically: each new path was checked against every path recorded so far, which got expensive for units with large local module sources, and monorepos paid that cost again for every unit and every command.

Recording a path now takes constant time no matter how many paths came before it, and re-marking already-recorded files is cheaper still. The reading lists reported by find and list are unchanged.