Replace per-site lambda generation with TriggerForwarder<Ts...>,
TriggerOnTrueForwarder, and TriggerOnFalseForwarder structs. The
compiler generates one operator() per forwarder type shared across
all call sites, avoiding flash duplication from unique lambdas.
Also cleans up API: replaces condition/callback_args with
bool_filter using TRIGGER_ON_TRUE/TRIGGER_ON_FALSE constants.