Szuru doesn't allow images with more than 178956970 pixels
Some very large images are not accepted by szurubooru, as the server thinks it is an attack:
```
[2024-06-17 10:48:11] waitress Exception while serving /post/501
Traceback (most recent call last):
File "/usr/lib/python3.8/site-packages/waitress/channel.py", line 350, in service
task.service()
File "/usr/lib/python3.8/site-packages/waitress/task.py", line 171, in service
self.execute()
File "/usr/lib/python3.8/site-packages/waitress/task.py", line 441, in execute
app_iter = self.channel.server.application(environ, start_response)
File "/opt/app/szurubooru/rest/app.py", line 104, in application
response = handler(ctx, match.groupdict())
File "/opt/app/szurubooru/api/post_api.py", line 127, in update_post
posts.update_post_content(
File "/opt/app/szurubooru/func/posts.py", line 646, in update_post_content
post.signature = generate_post_signature(post, content)
File "/opt/app/szurubooru/func/posts.py", line 551, in generate_post_signature
unpacked_signature = image_hash.generate_signature(content)
File "/opt/app/szurubooru/func/image_hash.py", line 229, in generate_signature
im_array = _preprocess_image(content)
File "/opt/app/szurubooru/func/image_hash.py", line 43, in _preprocess_image
img = Image.open(BytesIO(content))
File "/usr/lib/python3.8/site-packages/PIL/Image.py", line 2916, in open
im = _open_core(fp, filename, prefix)
File "/usr/lib/python3.8/site-packages/PIL/Image.py", line 2903, in _open_core
_decompression_bomb_check(im.size)
File "/usr/lib/python3.8/site-packages/PIL/Image.py", line 2826, in _decompression_bomb_check
raise DecompressionBombError(
PIL.Image.DecompressionBombError: Image size (191410768 pixels) exceeds limit of 178956970 pixels, could be decompression bomb DOS attack.
```
Changing this pixel count requires a custom image, as this variable is hardcoded into the code. https://github.com/rr-/szurubooru/issues/503 and https://github.com/rr-/szurubooru/issues/662 provide solutions on this.
issue