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/providers/remote/eval/nvidia/eval.py

@@ -3,7 +3,7 @@
 #
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
-from typing import Any, Dict, List
+from typing import Any
 
 import requests
 
@@ -101,8 +101,8 @@ class NVIDIAEvalImpl(
     async def evaluate_rows(
         self,
         benchmark_id: str,
-        input_rows: List[Dict[str, Any]],
-        scoring_functions: List[str],
+        input_rows: list[dict[str, Any]],
+        scoring_functions: list[str],
         benchmark_config: BenchmarkConfig,
     ) -> EvaluateResponse:
         raise NotImplementedError()