fix: don't crash pindexer on blocks without a timestamp (#4764)

## Describe your changes

this sets timestamp to default for blocks without one to

## Issue ticket number and link

fixes #4761

## Checklist before requesting a review

- [x] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

indexer changes only

crates/bin/pindexer/src/block.rs

@@ -40,9 +40,7 @@ CREATE TABLE IF NOT EXISTS block_details (
         _src_db: &PgPool,
     ) -> Result<(), anyhow::Error> {
         let pe = pb::EventBlockRoot::from_event(event.as_ref())?;
-        let timestamp = pe
-            .timestamp
-            .ok_or(anyhow!("block at height {} has no timestamp", pe.height))?;
+        let timestamp = pe.timestamp.unwrap_or_default();
 
         sqlx::query(
             "