RUE-1589: Account only inline scans that run

[steveklabnik]

Fixes RUE-1589

Summary:

• count only bodies whose inline constructor-head reachability scan actually runs
• validate pops as child edges plus scanned bodies, bounded by all precomputed bodies
• keep schema version 1 readable through an additive default and compatibility coverage
• cover the census-zero boundary regression

Validation:

• scripts/rue fmt
• scripts/rue quick
• scripts/rue premerge
• startup benchmark JSON smoke test