Use streams to download attachments directly to disk

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

ts/hooks/useScrollLock.tsx

@@ -4,7 +4,7 @@
 import { useContext, createContext, useEffect, useRef } from 'react';
 import * as log from '../logging/log';
 
-type ScrollerLock = Readonly<{
+export type ScrollerLock = Readonly<{
   isLocked(): boolean;
   lock(reason: string, onUserInterrupt: () => void): () => void;
   onUserInterrupt(reason: string): void;