Proc-macros for Yog inter-mod communication.
#[yog_export] on fn: generates a C-ABI wrapper and a ctor constructor
that registers it into yog_api's auto-export registry when the mod's
cdylib is loaded — export_mod! flushes that registry into
registry.interop().export(...) automatically, no manual call needed.
import! macro: generates Rust wrapper + binding slot.