This is a refactor of the codebase to use a more memory-efficient
representation of notes. It should also be much faster at decoding since
we're using a custom C json parser now.
Changelog-Changed: Improved memory usage and performance when processing events
This is needed for longform events. Right now we treat unseparated note
artifacts as a list of blocks, but we will likely need to render these
blocks into lists of attributed texts with image blocks inbetween.
