Eliminate popping when scrolling

This commit makes a few changes:

- Link preview views are no longer cached, only the metadata. This fixes
  a memory leak when preview videos. It will keep playing the video
  forever eventually leading to a crash. This is fixed!

- Cache the intrinsic height of previews, when loading notes it looks
  for the cached height so that things don't pop-in after the fact

- Note artifacts and previews are set in the constructor instead of
  onAppear, this prevents the size from changing and popping after it
  has been loaded into the lazyvstack

Changelog-Fixed: Fix memory leak with inline videos
Changelog-Fixed: Eliminate popping when scrolling

damus/Util/LinkView.swift

@@ -10,10 +10,11 @@ import LinkPresentation
 
 class CustomLinkView: LPLinkView {
     override var intrinsicContentSize: CGSize { CGSize(width: 0, height: super.intrinsicContentSize.height) }
+    
 }
 
 enum Metadata {
-    case linkmeta(LPLinkMetadata)
+    case linkmeta(CachedMetadata)
     case url(URL)
 }
 
@@ -26,12 +27,19 @@ struct LinkViewRepresentable: UIViewRepresentable {
     func makeUIView(context: Context) -> CustomLinkView {
         switch meta {
         case .linkmeta(let linkmeta):
-            return CustomLinkView(metadata: linkmeta)
+            return CustomLinkView(metadata: linkmeta.meta)
         case .url(let url):
             return CustomLinkView(url: url)
         }
     }
  
     func updateUIView(_ uiView: CustomLinkView, context: Context) {
+        switch meta {
+        case .linkmeta(let cached):
+            cached.intrinsic_height = uiView.intrinsicContentSize.height
+        case .url:
+            return
+        }
+        
     }
 }

damus/Util/PreviewCache.swift

@@ -8,8 +8,18 @@
 import Foundation
 import LinkPresentation
 
+class CachedMetadata {
+    let meta: LPLinkMetadata
+    var intrinsic_height: CGFloat?
+    
+    init(meta: LPLinkMetadata) {
+        self.meta = meta
+        self.intrinsic_height = nil
+    }
+}
+
 enum Preview {
-    case value(LinkViewRepresentable)
+    case value(CachedMetadata)
     case failed
 }
 
@@ -20,12 +30,12 @@ class PreviewCache {
         return previews[evid]
     }
     
-    func store(evid: String, preview: LinkViewRepresentable?)  {
+    func store(evid: String, preview: LPLinkMetadata?)  {
         switch preview {
         case .none:
             previews[evid] = .failed
         case .some(let meta):
-            previews[evid] = .value(meta)
+            previews[evid] = .value(CachedMetadata(meta: meta))
         }
     }