Add experimental setting to hide videos without duration in Invidious

This adds a new instance setting for Invidious that filters out videos
without duration information from feeds, popular, trending, search results,
and channel pages. This can be used to hide YouTube Shorts.

The setting is labeled as "Experimental: Hide videos without duration" and
includes an explanation that it can be used to hide shorts.

Key changes:
- Added hideVideosWithoutDuration property to Instance model
- Updated InstancesBridge to serialize/deserialize the new setting
- Added UI toggle in InstanceSettings with explanatory footer text
- Implemented filtering in InvidiousAPI for:
  * Popular videos
  * Trending videos
  * Search results
  * Subscription feed
  * Channel content
- Videos accessed directly by URL are not filtered

Model/Accounts/InstancesModel.swift

@@ -90,6 +90,17 @@ final class InstancesModel: ObservableObject {
         Defaults[.instances][index] = instance
     }
 
+    func setHideVideosWithoutDuration(_ instance: Instance, _ hideVideosWithoutDuration: Bool) {
+        guard let index = Defaults[.instances].firstIndex(where: { $0.id == instance.id }) else {
+            return
+        }
+
+        var instance = Defaults[.instances][index]
+        instance.hideVideosWithoutDuration = hideVideosWithoutDuration
+
+        Defaults[.instances][index] = instance
+    }
+
     func remove(_ instance: Instance) {
         let accounts = accounts(instance.id)
         if let index = Defaults[.instances].firstIndex(where: { $0.id == instance.id }) {