Function call_i64_export 

pub fn call_i64_export<T>(
    engine: &Engine,
    store: &mut Store<T>,
    module: &Module,
    export: &str,
) -> Result<i64, EngineError>

Instantiates module against an empty linker and calls a zero-arg export returning a single i64. Constraints (fuel cap, epoch deadline) come from the caller-supplied Store.