update to svelte 5

src/lib/components/PostComponent.svelte

@@ -6,15 +6,21 @@
   import { secondsSince, relativeTime } from '$lib/relativeTime';
   import { onMount } from 'svelte';
 
-  export let post: Post;
-  let displayRelativeTime = false;
-  const absoluteDate = new Date(post.created_at).toLocaleString();
-  let dateCreated = absoluteDate;
-  const timePassed = secondsSince(new Date(post.created_at));
-  $: if (displayRelativeTime) {
-    dateCreated = relativeTime($timePassed) ?? absoluteDate;
+  interface Props {
+    post: Post;
   }
 
+  let { post }: Props = $props();
+  let displayRelativeTime = $state(false);
+  const absoluteDate = new Date(post.created_at).toLocaleString();
+  const timePassed = secondsSince(new Date(post.created_at));
+  let dateCreated = $derived.by(() => {
+    if (displayRelativeTime) {
+      return relativeTime($timePassed) ?? absoluteDate;
+    }
+    return absoluteDate;
+  });
+
   const songs = filterDuplicates(post.songs ?? []);
 
   function filterDuplicates(songs: SongInfo[]): SongInfo[] {