Typescript migration part 2 (#261)

Converts everything to typescript, adding `@ts-expect-error`s where
necessary. Also makes some progress converting elements to use
decorators, but we're not fully there yet — I think it'll make sense to
continue to do that in future PRs, rather than doing it all in one go,
just so that we can keep up with the dev branch.

src/types.ts

@@ -8,6 +8,8 @@ export interface Item {
    * Archived Item ID
    */
   coll?: string;
+  // TODO(emma) is `id` the same as `coll`? should they be merged?
+  id?: string;
   name?: string;
   title?: string;
   loadUrl?: string;
@@ -24,9 +26,11 @@ export interface Item {
     software?: string;
   };
   onDemand?: boolean;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO fixme
   pages?: any[];
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO fixme
   lists?: any[];
   ctime?: string;
   totalSize?: unknown;
-  size?: unknown;
+  size?: number | string;
 }