Split safety into (llama-guard, prompt-guard, code-scanner) (#400)

Splits the meta-reference safety implementation into three distinct providers:

- inline::llama-guard
- inline::prompt-guard
- inline::code-scanner

Note that this PR is a backward incompatible change to the llama stack server. I have added deprecation_error field to ProviderSpec -- the server reads it and immediately barfs. This is used to direct the user with a specific message on what action to perform. An automagical "config upgrade" is a bit too much work to implement right now :/

(Note that we will be gradually prefixing all inline providers with inline:: -- I am only doing this for this set of new providers because otherwise existing configuration files will break even more badly.)

llama_stack/distribution/server/server.py

@@ -9,6 +9,7 @@ import functools
 import inspect
 import json
 import signal
+import sys
 import traceback
 
 from contextlib import asynccontextmanager
@@ -41,7 +42,7 @@ from llama_stack.providers.utils.telemetry.tracing import (
 )
 from llama_stack.distribution.datatypes import *  # noqa: F403
 from llama_stack.distribution.request_headers import set_request_provider_data
-from llama_stack.distribution.resolver import resolve_impls
+from llama_stack.distribution.resolver import InvalidProviderError, resolve_impls
 
 from .endpoints import get_all_api_endpoints
 
@@ -282,7 +283,13 @@ def main(
 
     dist_registry, dist_kvstore = asyncio.run(create_dist_registry(config))
 
-    impls = asyncio.run(resolve_impls(config, get_provider_registry(), dist_registry))
+    try:
+        impls = asyncio.run(
+            resolve_impls(config, get_provider_registry(), dist_registry)
+        )
+    except InvalidProviderError:
+        sys.exit(1)
+
     if Api.telemetry in impls:
         setup_logger(impls[Api.telemetry])