Require ObservableScopes of state holders to be specified explicitly

Previously we had a ViewModel class which was responsible for little more than creating an ObservableScope. However, since this ObservableScope would be created implicitly upon view model construction, it became a tad bit harder for callers to remember to eventually end the scope (as you wouldn't just have to remember to end ObservableScopes, but also to destroy ViewModels). Requiring the scope to be specified explicitly by the caller also makes it possible for the caller to reuse the scope for other purposes, reducing the number of scopes mentally in flight that need tending to, and for all state holders (not just view models) to be handled uniformly by helper functions such as generateKeyed$.

src/state/ScreenShare.ts

@@ -11,7 +11,7 @@ import {
   type Room as LivekitRoom,
 } from "livekit-client";
 
-import { ObservableScope } from "./ObservableScope.ts";
+import { type ObservableScope } from "./ObservableScope.ts";
 import { ScreenShareViewModel } from "./MediaViewModel.ts";
 import type { RoomMember } from "matrix-js-sdk";
 import type { EncryptionSystem } from "../e2ee/sharedKeyManagement.ts";
@@ -23,10 +23,10 @@ import type { Behavior } from "./Behavior.ts";
  * ObservableScope for behaviors that the view model depends on.
  */
 export class ScreenShare {
-  private readonly scope = new ObservableScope();
   public readonly vm: ScreenShareViewModel;
 
   public constructor(
+    private readonly scope: ObservableScope,
     id: string,
     member: RoomMember,
     participant: LocalParticipant | RemoteParticipant,
@@ -37,6 +37,7 @@ export class ScreenShare {
     displayName$: Observable<string>,
   ) {
     this.vm = new ScreenShareViewModel(
+      this.scope,
       id,
       member,
       of(participant),
@@ -48,9 +49,4 @@ export class ScreenShare {
       participant.isLocal,
     );
   }
-
-  public destroy(): void {
-    this.scope.end();
-    this.vm.destroy();
-  }
 }