Macro define_direct_function

macro_rules! define_direct_function {
    ($name:ident, args: [], $body:expr) => { ... };
    ($name:ident, args: [$arg_type:ty], $body:expr) => { ... };
    ($name:ident, args: [$arg_type1:ty, $arg_type2:ty], $body:expr) => { ... };
    ($name:ident, args: [$arg_type1:ty, $arg_type2:ty, $arg_type3:ty], $body:expr) => { ... };
    ($name:ident, args: [$arg_type1:ty, $arg_type2:ty, $arg_type3:ty, $arg_type4:ty], $body:expr) => { ... };
}

Macro for functions that return direct values (not Result<T, E>) Uses convert_result_to_value() for direct value types