chore: Change moderations api response to Provider returned categories (#3098)

# What does this PR do?
To be compliant with model policies for LLAMA, just return the
categories as is from provider, we will lose the OAI compat in
moderations api response.

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## Test Plan
`SAFETY_MODEL=llama-guard3:8b LLAMA_STACK_CONFIG=starter uv run pytest
-v tests/integration/safety/test_safety.py
--text-model=llama3.2:3b-instruct-fp16
--embedding-model=all-MiniLM-L6-v2 --safety-shield=ollama`

llama_stack/providers/inline/safety/prompt_guard/prompt_guard.py

@@ -18,6 +18,7 @@ from llama_stack.apis.safety import (
     ShieldStore,
     ViolationLevel,
 )
+from llama_stack.apis.safety.safety import ModerationObject
 from llama_stack.apis.shields import Shield
 from llama_stack.core.utils.model_utils import model_local_dir
 from llama_stack.providers.datatypes import ShieldsProtocolPrivate
@@ -64,8 +65,8 @@ class PromptGuardSafetyImpl(Safety, ShieldsProtocolPrivate):
 
         return await self.shield.run(messages)
 
-    async def run_moderation(self, input: str | list[str], model: str):
-        raise NotImplementedError("run_moderation not implemented for PromptGuard")
+    async def run_moderation(self, input: str | list[str], model: str) -> ModerationObject:
+        raise NotImplementedError("run_moderation is not implemented for Prompt Guard")
 
 
 class PromptGuardShield: