Increase threshold of large account in diff-states

This commit increases the minimum payload count threshold for
large accounts to use extra goroutines.  So only the largest
accounts that would benefit most from extra goroutines use them.

The minimum payload count was 50,000 and was increased to 1 million.

cmd/util/ledger/migrations/cadence_value_diff.go

@@ -76,7 +76,7 @@ type difference struct {
 	NewValueStaticType string `json:",omitempty"`
 }
 
-const minLargeAccountRegisterCount = 50_000
+const minLargeAccountRegisterCount = 1_000_000
 
 type CadenceValueDiffReporter struct {
 	address        common.Address