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/inline/telemetry/meta_reference/config.py

@@ -5,7 +5,7 @@
 # the root directory of this source tree.
 
 from enum import Enum
-from typing import Any, Dict, List
+from typing import Any
 
 from pydantic import BaseModel, Field, field_validator
 
@@ -33,7 +33,7 @@ class TelemetryConfig(BaseModel):
         default="",
         description="The service name to use for telemetry",
     )
-    sinks: List[TelemetrySink] = Field(
+    sinks: list[TelemetrySink] = Field(
         default=[TelemetrySink.CONSOLE, TelemetrySink.SQLITE],
         description="List of telemetry sinks to enable (possible values: otel, sqlite, console)",
     )
@@ -50,7 +50,7 @@ class TelemetryConfig(BaseModel):
         return v
 
     @classmethod
-    def sample_run_config(cls, __distro_dir__: str, db_name: str = "trace_store.db") -> Dict[str, Any]:
+    def sample_run_config(cls, __distro_dir__: str, db_name: str = "trace_store.db") -> dict[str, Any]:
         return {
             "service_name": "${env.OTEL_SERVICE_NAME:}",
             "sinks": "${env.TELEMETRY_SINKS:console,sqlite}",