feat(tests): Improve unit test coverage for Studio services

I noticed that the test coverage for services is quite limited. Currently, only 4 out of 14 services in `services` have unit tests:

Better test coverage would:
- Make it safer to refactor code without accidentally breaking things
- Help catch bugs before they reach production

The existing tests follow a nice pattern using `createServices()`, so it would be straightforward to add more tests following the same approach

**What changes have to be introduced?**
Add unit test files for the untested services.

**Will this be a breaking change?**
No, this only adds new test files. No changes to existing code or APIs.

Services without tests:
- `parser.service.ts`
- `app.service.ts`
- `specification.service.ts`
- `settings.service.ts`
- `monaco.service.ts`, `preview.service.tsx`, `socket-client.service.tsx`, `server-api.service.ts`

One thing that can also be done here is that to break this issue into multiple prs . If this approach seems valid , i would be happy to complete this issue

Inspect the existing service unit tests and the `createServices()` pattern first, then review the listed untested services: `parser.service.ts`, `app.service.ts`, `specification.service.ts`, `settings.service.ts`, `monaco.service.ts`, `preview.service.tsx`, `socket-client.service.tsx`, and `server-api.service.ts`. Done means adding unit test files for the untested services without changing existing code or APIs, with the test suite passing.

Written by the indexing model from the issue text.