Function logos_rt_alloc_list_i64_fixed 

pub unsafe extern "C" fn logos_rt_alloc_list_i64_fixed(
    frame: *mut i64,
    vec_slot: i64,
    ptr_slot: i64,
    len_slot: i64,
)

Allocate a proof-sized Int list. The adapter places the capacity in len_slot; this helper consumes it and restores the observable length 0.