Function create_defuns 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn create_defuns() -> *const Defuns

Creates an empty Defun (a list of user-defined functions).

Defuns are used to pass user-defined functions (either Python functions or symjit-compiled functions).

Safety

It returns a pointer to the allocated Defun, which needs to be
deallocated eventually.