chore: enable pyupgrade fixes (#1806)

# What does this PR do?

The goal of this PR is code base modernization.

Schema reflection code needed a minor adjustment to handle UnionTypes
and collections.abc.AsyncIterator. (Both are preferred for latest Python
releases.)

Note to reviewers: almost all changes here are automatically generated
by pyupgrade. Some additional unused imports were cleaned up. The only
change worth of note can be found under `docs/openapi_generator` and
`llama_stack/strong_typing/schema.py` where reflection code was updated
to deal with "newer" types.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

llama_stack/apis/safety/safety.py

@@ -5,7 +5,7 @@
 # the root directory of this source tree.
 
 from enum import Enum
-from typing import Any, Dict, List, Optional, Protocol, runtime_checkable
+from typing import Any, Protocol, runtime_checkable
 
 from pydantic import BaseModel, Field
 
@@ -27,16 +27,16 @@ class SafetyViolation(BaseModel):
     violation_level: ViolationLevel
 
     # what message should you convey to the user
-    user_message: Optional[str] = None
+    user_message: str | None = None
 
     # additional metadata (including specific violation codes) more for
     # debugging, telemetry
-    metadata: Dict[str, Any] = Field(default_factory=dict)
+    metadata: dict[str, Any] = Field(default_factory=dict)
 
 
 @json_schema_type
 class RunShieldResponse(BaseModel):
-    violation: Optional[SafetyViolation] = None
+    violation: SafetyViolation | None = None
 
 
 class ShieldStore(Protocol):
@@ -52,6 +52,6 @@ class Safety(Protocol):
     async def run_shield(
         self,
         shield_id: str,
-        messages: List[Message],
-        params: Dict[str, Any] = None,
+        messages: list[Message],
+        params: dict[str, Any] = None,
     ) -> RunShieldResponse: ...