complexity: pair duplicate function keys instead of collapsing them

file+name is not unique within a tree: a file may declare several func init() and any number of func _(), and the CSVs name them all alike. Collapsing base duplicates to their maximum let a new over-limit init pass the gate by hiding behind a heavier legacy twin in the same file. Occurrences sharing a key now pair worst-with-worst, so the extra head occurrence has no counterpart and fails as new.