Fix indexer get checkpoint e2e (MystenLabs#9843)

## Description 

Looks like Checkpoint sequence number is a `BigInt` now

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

crates/sui-indexer/tests/integration_tests.rs

@@ -1063,14 +1063,14 @@ pub mod pg_integration_test {
         // Allow indexer to sync
         wait_until_next_checkpoint(&store).await;
         let current_epoch = store.get_current_epoch().unwrap();
-        let cp = store.get_latest_checkpoint_sequence_number().unwrap();
+        let cp = store.get_latest_checkpoint_sequence_number().unwrap() as u64;
         let first_checkpoint = indexer_rpc_client
             .get_checkpoint(CheckpointId::SequenceNumber(cp.try_into().unwrap()))
             .await
             .unwrap();
 
         assert_eq!(first_checkpoint.epoch, current_epoch.epoch);
-        assert_eq!(first_checkpoint.sequence_number, 0);
+        assert_eq!(u64::from(first_checkpoint.sequence_number), 0);
         assert_eq!(first_checkpoint.network_total_transactions, 1);
         assert_eq!(first_checkpoint.previous_digest, None);
         assert_eq!(first_checkpoint.transactions.len(), 1);
@@ -1089,22 +1089,28 @@ pub mod pg_integration_test {
             .await?;
         let next_cp = tx_response.checkpoint.unwrap();
         let next_checkpoint = indexer_rpc_client
-            .get_checkpoint(CheckpointId::SequenceNumber(next_cp))
+            .get_checkpoint(CheckpointId::SequenceNumber(next_cp.try_into().unwrap()))
             .await?;
         let current_epoch = store.get_current_epoch().unwrap();
 
         assert_eq!(next_checkpoint.epoch, current_epoch.epoch);
-        assert!(next_checkpoint.sequence_number > first_checkpoint.sequence_number);
+        assert!(
+            u64::from(next_checkpoint.sequence_number)
+                > u64::from(first_checkpoint.sequence_number)
+        );
         assert!(
             next_checkpoint.network_total_transactions
                 > first_checkpoint.network_total_transactions
         );
         assert!(next_checkpoint.transactions.contains(&tx_response.digest));
 
         let mut curr_checkpoint = next_checkpoint;
-        for i in (first_checkpoint.sequence_number..curr_checkpoint.sequence_number).rev() {
+        for i in (u64::from(first_checkpoint.sequence_number)
+            ..u64::from(curr_checkpoint.sequence_number))
+            .rev()
+        {
             let prev_checkpoint = indexer_rpc_client
-                .get_checkpoint(CheckpointId::SequenceNumber(i))
+                .get_checkpoint(CheckpointId::SequenceNumber(i.try_into().unwrap()))
                 .await?;
             assert_eq!(
                 curr_checkpoint.previous_digest,