Render large image files to disk

This will make little difference to the render process, but saves them to disk once the generation is complete to help clean up memory faster.

wagtail/images/models.py

@@ -4,7 +4,7 @@ import os.path
 import time
 from collections import OrderedDict
 from contextlib import contextmanager
-from io import BytesIO
+from tempfile import SpooledTemporaryFile
 from typing import Union
 
 import willow
@@ -538,7 +538,10 @@ class AbstractImage(ImageFileMixin, CollectionMember, index.Indexed, models.Mode
         start_time = time.time()
 
         try:
-            generated_image = filter.run(self, BytesIO())
+            generated_image = filter.run(
+                self,
+                SpooledTemporaryFile(max_size=settings.FILE_UPLOAD_MAX_MEMORY_SIZE),
+            )
 
             logger.debug(
                 "Generated '%s' rendition for image %d in %.1fms",