Optimize json processing and preloading

- Preload events when added to the EventHolder queue
- Remove relative time formatting from preloader. Just do it when event appears
- Process incoming json in a background queue by default

Changelog-Fixed: Fix wrong relative times on events
Changelog-Changed: Preload events when they are queued

damus/Views/Timeline/InnerTimelineView.swift

@@ -64,7 +64,7 @@ struct InnerTimelineView: View {
                                    indexed[safe: ind+5]?.0
                                   ].compactMap({ $0 }))
                             
-                            preload_events(event_cache: state.events, events: to_preload, profiles: state.profiles, our_keypair: state.keypair, settings: state.settings)
+                            preload_events(state: state, events: to_preload)
                         }
                     
                     ThiccDivider()