See T110692 which is now fixed on the Parsoid end by adding type-conversion code for image into responses. It is worth fixing this in the batching api extension so that it returns numbers instead of strings for image dimensions. See comment in https://gerrit.wikimedia.org/r/#/c/226670/2/includes/ApiParsoidBatch.php
Once done, we should remove the type-conversion code in Parsoid added as part of the fix for T110692