Fix up benchmark harness and test data

implementations/rust/preserves/benches/codec.rs

@@ -91,6 +91,7 @@ pub fn large_testdata_decoder_with_ann(c: &mut Criterion) {
         b.iter(|| {
             let mut src = BytesBinarySource::new(&bs[..]);
             let mut r = src.packed();
+            r.open_sequence().unwrap();
             while let Some(_) = r.next_iovalue(true).unwrap() {}
         })
     });
@@ -104,6 +105,7 @@ pub fn large_testdata_decoder_without_ann(c: &mut Criterion) {
         b.iter(|| {
             let mut src = BytesBinarySource::new(&bs[..]);
             let mut r = src.packed();
+            r.open_sequence().unwrap();
             while let Some(_) = r.next_iovalue(false).unwrap() {}
         })
     });
@@ -115,6 +117,7 @@ pub fn large_testdata_encoder(c: &mut Criterion) {
         let mut vs = vec![];
         let mut src = IOBinarySource::new(&mut fh);
         let mut r = src.packed();
+        r.open_sequence().unwrap();
         while let Some(v) = r.next_iovalue(true).unwrap() {
             vs.push(v);
         }