GamConfig
Configuration for Google Ad Manager pod serving.
Presence is the OPT-IN: constructing a GamConfig (even an empty one) is what tells the SDK this integration wires IMA. It carries only client-side tuning — the stream identity (networkCode + customAssetKey) comes from the break manifest's vendorConfiguration, so that a client and its backend can no longer disagree about which GAM asset the pods belong to.