Sortal_feed.MetaPer-feed sync metadata.
Tracks last-sync time, HTTP conditional GET headers, and entry count for each feed file. Stored as JSON alongside the feed data.
type t = {feed_url : string;feed_type : Sortal_schema.Feed.feed_type;last_sync : Ptime.t option;etag : string option;last_modified : string option;entry_count : int;}val save : Eio.Fs.dir_ty Eio.Path.t -> t -> unitval load : Eio.Fs.dir_ty Eio.Path.t -> t option