Function plan_fixes 

pub fn plan_fixes(
    source: &str,
    fixes: Vec<Fix>,
    allowed_applicability: &[FixApplicability],
    protected_ranges: &[ProtectedRange],
) -> PlanResult

Plan fixes deterministically and collect blocked reasons.

Order is deterministic by: priority, first edit start, rule_code, then additional stable tie-breakers.

If allowed_applicability is empty, all applicability classes are allowed.