Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

src/presentation/components/TheFooter/DownloadUrlListItem.vue

@@ -39,7 +39,7 @@ export default defineComponent({
       return hasDesktopVersion(props.operatingSystem);
     });
 
-    const downloadUrl = computed<string | undefined>(() => {
+    const downloadUrl = computed<string>(() => {
       return info.getDownloadUrl(props.operatingSystem);
     });