feat(engine): don't iterate over deleted keys

When iterating in an open transaction, we would create an iterator containing all entries in the database as well as the entries in the transaction cache. This ensures any keys added in the same transaction are also encountered during iterating.

We do not do anything with the keys that are deleted within the transaction. As a result, when iterating we will go over keys that are already deleted. This is wrong. The keys are deleted, so we should not encounter them anymore during iterating.

(cherry picked from commit 84be02b)

engine/src/main/java/io/camunda/zeebe/process/test/engine/db/InMemoryDbTransaction.java

@@ -100,6 +100,7 @@ public InMemoryDbIterator newIterator() {
     final TreeMap<Bytes, Bytes> snapshot = new TreeMap<>();
     snapshot.putAll(database);
     snapshot.putAll(transactionCache);
+    deletedKeys.forEach(snapshot::remove);
 
     return new InMemoryDbIterator(snapshot);
   }