test: revamp eval related integration tests (#1433)

# What does this PR do?
- revamp and clean up datasets/scoring/eval integration tests
- closes https://github.com/meta-llama/llama-stack/issues/1396

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan
**dataset**
```
LLAMA_STACK_BASE_URL=http://localhost:8321 pytest -v tests/integration/datasetio/
```
<img width="842" alt="image"
src="https://github.com/user-attachments/assets/88fc2b6a-b496-47bf-bc0c-8fea48ba36ff"
/>

**scoring**
```
LLAMA_STACK_CONFIG=fireworks pytest -v tests/integration/scoring --text-model meta-llama/Llama-3.1-8B-Instruct --judge-model meta-llama/Llama-3.1-8B-Instruct
```
<img width="851" alt="image"
src="https://github.com/user-attachments/assets/50f46415-b44c-4c37-a6c3-076f2767adb3"
/>


**eval**
```
LLAMA_STACK_CONFIG=fireworks pytest -v tests/integration/eval --text-model meta-llama/Llama-3.1-8B-Instruct --judge-model meta-llama/Llama-3.1-8B-Instruct
```
<img width="841" alt="image"
src="https://github.com/user-attachments/assets/8eb1c65c-3b39-4d66-8ff4-f471ca783e49"
/>


[//]: # (## Documentation)

tests/integration/conftest.py

@@ -59,7 +59,7 @@ def pytest_addoption(parser):
     )
     parser.addoption(
         "--judge-model",
-        help="comma-separated list of judge models. Fixture name: judge_model_id",
+        help="Specify the judge model to use for testing",
     )
     parser.addoption(
         "--embedding-dimension",