ACE_GetContraptionEntities

Collect entities belonging to a contraption. BILLING RULE: every entity prices in exactly ONE contraption -- its own. The one exception: a gun/rack with no contraption of its own (parent-only builds) is adopted by its link anchor's contraption (above). This keeps link-only weapons priced without double-billing: a weapon reachable from two fragments (its own turret + the hull holding its crates) must bill to exactly one contraption, not both. Do NOT walk the AmmoLink/Master graph outward to gather members -- that reaches such a weapon from both fragments and prices it in each, inflating Firepower and Engine totals.