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
Since we can't mutate NdbNotes, let's update the existing codebase to
generate and sign ids on NostrEvent constructions. This will allow us to
match NdbNote's constructor
