Enable the no-undef eslint rule (#1848)

## Description:

Enable the `no-undef` eslint rule.

Fixes #1786

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

src/client/InputHandler.ts

@@ -129,7 +129,7 @@ export class InputHandler {
 
   private alternateView = false;
 
-  private moveInterval: NodeJS.Timeout | null = null;
+  private moveInterval: ReturnType<typeof setTimeout> | null = null;
   private activeKeys = new Set<string>();
   private keybinds: Record<string, string> = {};