project.get_labeled_tasks API returns BROKEN json

**Describe the bug**
NB: This could be a "feature" and not a "bug" since how obviously it is "broken". Perhaps I'm mis-using API and have wrong expectations of it.

This commit line deliberately breaks parsable json:
https://github.com/HumanSignal/label-studio/commit/c65330c0#diff-7ce60240b37e69943356ab25fe22bef989b3eed3066f58372bdfd8edb029b6dbR222

**To Reproduce**
```python
from label_studio_sdk import Client
import json

LABEL_STUDIO_URL = 'http://localhost:8080'
API_KEY = '***'

ls = Client(url=LABEL_STUDIO_URL, api_key=API_KEY)

json.loads(ls.get_project(1).get_labeled_tasks()[0]['annotations_results'])
>JSONDecodeError
```

**Expected behavior**

json is parsed

**Additional context**

I understand the motivation of that PR, which was to "speed up" slow execution. Changes like "json -> ujson" were introduced. But at the same time, modifying "annotations_results" field this way makes it practically unusable. Perhaps the intention that this API would be used in UI, and NOT for accessing "annotations_results" programmatically. If that's the case - then perhaps there should be alternative way to retrieve FULL results, perhaps with pagination.