core/rawdb: update freezertable read meter (ethereum#26946)

The meter for "for measuring the effective amount of data read" within the freezertable was never updated. This change remedies that. 
---------

Signed-off-by: jsvisa <delweng@gmail.com>

core/rawdb/freezer_table.go

@@ -823,6 +823,9 @@ func (t *freezerTable) retrieveItems(start, count, maxBytes uint64) ([]byte, []i
 			break
 		}
 	}
+
+	// Update metrics.
+	t.readMeter.Mark(int64(totalSize))
 	return output[:outputSize], sizes, nil
 }