Previously the page-based (numbered) paginator would always count the
total_pages, even in API calls when it wasn't needed. This could be very
slow in some cases. Refactor so that total_pages isn't calculated unless
it's called.
While we're at it, refactor to condense all the sequential vs. numbered
pagination logic into one module. This incidentally fixes a couple more
bugs:
* "page=b0" returned all pages rather than nothing.
* Bad parameters like "page=blaha123" and "page=a123blah" were accepted.
DEPRECATION WARNING: Initialization autoloaded the constants
Danbooru::Paginator and Danbooru::Paginator::ActiveRecordExtension.
Being able to do this is deprecated. Autoloading during
initialization is going to be an error condition in future versions
of Rails.
Reloading does not reboot the application, and therefore code
executed during initialization does not run again. So, if you reload
Danbooru::Paginator, for example, the expected changes won't be
reflected in that stale Module object.
`config.autoloader` is set to `classic`. These autoloaded constants
would have been unloaded if `config.autoloader` had been set to
`:zeitwerk`.
Please, check the "Autoloading and Reloading Constants" guide for
solutions.
