indexer-alt: fix field count for wal_ types (#20540)

## Description 

```
    // Add one here for cp_sequence_number field, because StoredObjectUpdate is used for
    // wal_* handlers, where the actual type has an additional field besides fields of T.
```

## Test plan 

Ci, we will want to add a test for chunk size <> commit limit, and will
do that in a separate pr.

---

## Release notes

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that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API:

crates/sui-indexer-alt/src/models/objects.rs

@@ -111,7 +111,9 @@ pub struct StoredWalObjType {
 
 /// StoredObjectUpdate is a wrapper type, we want to count the fields of the inner type.
 impl<T: FieldCount> FieldCount for StoredObjectUpdate<T> {
-    const FIELD_COUNT: usize = T::FIELD_COUNT;
+    // Add one here for cp_sequence_number field, because StoredObjectUpdate is used for
+    // wal_* handlers, where the actual type to commit has an additional field besides fields of T.
+    const FIELD_COUNT: usize = T::FIELD_COUNT.saturating_add(1);
 }
 
 impl<DB: Backend> serialize::ToSql<SmallInt, DB> for StoredOwnerKind