Function build_dependency_plan 

pub fn build_dependency_plan<'a, I>(
    sheet_reg: &mut SheetRegistry,
    formulas: I,
    policy: &CollectPolicy,
    volatile_flags: Option<&[bool]>,
) -> Result<DependencyPlan, ExcelError>
where
    I: Iterator<Item = (&'a str, u32, u32, &'a ASTNode)>,

Build a compact dependency plan from ASTs without mutating the graph. Sheets referenced by name are resolved/created through SheetRegistry at plan time.