feat(eval api): (2.2/n) delete eval / scoring / scoring_fn apis (#1700)

# What does this PR do?
- To make it easier, delete existing `eval/scoring/scoring_function`
apis. There will be a bunch of broken impls here. The sequence is:
1. migrate benchmark graders
2. clean up existing scoring functions

- Add a skeleton evaluation impl to make tests pass. 

## Test Plan
tested in following PRs

[//]: # (## Documentation)

llama_stack/templates/meta-reference-gpu/meta_reference.py

@@ -30,9 +30,7 @@ def get_distribution_template() -> DistributionTemplate:
         "safety": ["inline::llama-guard"],
         "agents": ["inline::meta-reference"],
         "telemetry": ["inline::meta-reference"],
-        "eval": ["inline::meta-reference"],
         "datasetio": ["remote::huggingface", "inline::localfs"],
-        "scoring": ["inline::basic", "inline::llm-as-judge", "inline::braintrust"],
         "tool_runtime": [
             "remote::brave-search",
             "remote::tavily-search",