fix: native FriReducedOpeningRecord size calculation (#1905)

The size of `a_prev_buf` (i.e. `a_prev_size`) was not being factored in
the size calculation for `FriReducedOpeningRecordMut`, sometimes making
the record too small.

Author: teokitan

extensions/native/circuit/src/fri/mod.rs

@@ -676,6 +676,9 @@ impl<F> SizedRecord<FriReducedOpeningLayout> for FriReducedOpeningRecordMut<'_,
     fn size(layout: &FriReducedOpeningLayout) -> usize {
         let mut total_len = size_of::<FriReducedOpeningHeaderRecord>();
         total_len += layout.metadata.length * size_of::<FriReducedOpeningWorkloadRowRecord<F>>();
+        if !layout.metadata.is_init {
+            total_len += layout.metadata.length * size_of::<F>();
+        }
         total_len += size_of::<FriReducedOpeningCommonRecord<F>>();
         total_len
     }