fix: Implement missing run_moderation method in PromptGuardSafetyImpl

[Elbehery]

What does this PR do?

This PR addresses an issue where PromptGuardSafetyImpl was an incomplete implementation of an abstract class. The class was missing the required run_moderation method from its parent interface.

Currently, running pre-commit locally fails with the error below.

llama_stack/providers/inline/safety/prompt_guard/__init__.py:15: error: Cannot instantiate abstract class "PromptGuardSafetyImpl" with abstract attribute "run_moderation"  [abstract]
Found 1 error in 1 file (checked 410 source files)

This PR fixes the issue as follows

• Added the missing run_moderation method to PromptGuardSafetyImpl
• Method raises NotImplementedError with appropriate message indicating this functionality is not implemented for PromptGuard
• This allows the class to be properly instantiated while clearly indicating the limitation

[nathan-weinberg]

Strange as pre-commit was passing in #2678 which was the last PR to modify this file

Thanks for the fix!

[ashwinb]

thx

[ashwinb]

cc @slekkala1

[r3v5]

Hey @Elbehery! I pulled from main, did rebase on my branch and still have this issue:

git commit -m "refactor: modify DELETE API endpoints by returning HTTP 204 No Content + empty body instead of 200 OK + response body with null"                                                                                                                                 ─╯
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mypy.........................................................................Failed
- hook id: mypy
- exit code: 1

llama_stack/providers/inline/safety/prompt_guard/__init__.py:15: error: Cannot instantiate abstract class "PromptGuardSafetyImpl" with abstract attribute "run_moderation"  [abstract]
Found 1 error in 1 file (checked 403 source files)

Distribution Template Codegen............................(no files to check)Skipped
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API Spec Codegen.........................................(no files to check)Skipped
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Check for missing __init__.py files..........................................Passed
Block @pytest.mark.asyncio and @pytest_asyncio.fixture.......................Passed
Generate CI documentation................................(no files to check)Skipped

╭─    ~/GitHub/llama-stack    modify-delet…eturning-204 *4 +2 ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 1 ✘  3s     16:39:57  ─╮
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[r3v5]

Alright, it works now!