refactor: standardise helper & fix types checks

- Standardise helper's function signature and body
  To match what is generated by default when creating a new helper.

- Fix types errors provided by implicit TypeScript checks
  This will help whenever the project is migrated to TS

addon/helpers/reading-time.js

@@ -2,18 +2,19 @@ import { helper } from '@ember/component/helper';
 import readingTime from 'reading-time';
 import humanizeDuration from 'humanize-duration';
 
-export default helper((params /*, hash*/) => {
-  let stats = readingTime(params[0] ?? '');
-  let options = params[1];
+export default helper(function helperReadingTime(positional /*, named*/) {
+  const stats = readingTime(String(positional[0]));
+  const userOptions = positional[1];
+
+  const defaultOptions = {
+    round: true,
+    /** @type {['m']} */
+    units: ['m'],
+    language: 'en',
+  };
+
   return humanizeDuration(
     stats.time < 60000 ? 60000 : stats.time,
-    Object.assign(
-      {
-        round: true,
-        units: ['m'],
-        language: 'en',
-      },
-      options
-    )
+    Object.assign({}, defaultOptions, userOptions)
   );
 });