Remove the Downloads::File class. Move download methods to
Danbooru::Http instead. This means that:
* HTTParty has been replaced with http.rb for downloading files.
* Downloading is no longer tightly coupled to source strategies. Before
Downloads::File tried to automatically look up the source and download
the full size image instead if we gave it a sample url. Now we can
do plain downloads without source strategies altering the url.
* The Cloudflare Polish check has been changed from checking for a
Cloudflare IP to checking for the CF-Polished header. Looking up the
list of Cloudflare IPs was slow and flaky during testing.
* The SSRF protection code has been factored out so it can be used for
normal http requests, not just for downloads.
* The Webmock gem can be removed, since it was only used for stubbing
out certain HTTParty requests in the download tests. The Webmock gem
is buggy and caused certain tests to fail during CI.
* The retriable gem can be removed, since we no longer autoretry failed
downloads. We assume that if a download fails once then retrying
probably won't help.
Fixes an exception when attempting to upload a Pixiv image from a
deleted work. The download strategy tries to fetch the source data in
the course of rewriting the URL, which fails if the work has been
deleted from Pixiv.
Raise a BadIDError and leave the URL as-is (don't rewrite it).
* Test that downloading the HTML page downloads the full size image
instead.
* Test that downloading a small or medium size image downloads the
full size instead.
* Test the above for both single illustrations and for manga galleries,
for new and old posts (i.e. uploaded before the Pixiv URL changes versus
after), and for different file extensions.
* Test trying to download ugoira zip files. These tests are expected to
fail because we don't support ugoira yet.
* Also add some more tests for fetching source data.
