fix[codegen]: fix double eval in dynarray append/pop (#4030)

append/pop does not have an eval once fence for the cases where it is in
memory. add a fence.

vyper/codegen/core.py

@@ -401,7 +401,8 @@ def append_dyn_array(darray_node, elem_node):
             )
 
             # store new length
-            ret.append(STORE(darray_node, ["add", len_, 1]))
+            ret.append(ensure_eval_once("append_dynarray", STORE(darray_node, ["add", len_, 1])))
+
             return IRnode.from_list(b1.resolve(b2.resolve(ret)))
 
 
@@ -415,7 +416,7 @@ def pop_dyn_array(darray_node, return_popped_item):
 
         with new_len.cache_when_complex("new_len") as (b2, new_len):
             # store new length
-            ret.append(STORE(darray_node, new_len))
+            ret.append(ensure_eval_once("pop_dynarray", STORE(darray_node, new_len)))
 
             # NOTE skip array bounds check bc we already asserted len two lines up
             if return_popped_item: