ndb: switch to nostrdb notes

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

nostrdb/nostrdb.c

@@ -521,6 +521,8 @@ static int ndb_builder_make_json_str(struct ndb_builder *builder,
 {
 	// let's not care about de-duping these. we should just unescape
 	// in-place directly into the strings table. 
+	if (written)
+		*written = len;
 
 	const char *p, *end, *start;
 	unsigned char *builder_start;