refactor(anthropic): type the responses refusal stream iterator state

Types the cached sync upstream iterator instead of holding it as Any, so the
Responses to Anthropic streaming wrapper carries no untyped state.

litellm/llms/anthropic/experimental_pass_through/responses_adapters/streaming_iterator.py

@@ -4,7 +4,7 @@ import asyncio
 import json
 import traceback
 from collections import deque
-from collections.abc import AsyncIterator, Mapping
+from collections.abc import AsyncIterator, Iterator, Mapping
 from typing import TYPE_CHECKING, Any, Final
 
 from litellm import verbose_logger
@@ -55,7 +55,7 @@ class AnthropicResponsesStreamWrapper:
         self._sent_message_stop = False
         self._chunk_queue: deque[dict[str, object]] = deque()
         self._refusal_text_parts: list[str] = []  # mutable-ok: accumulates streamed refusal delta text across chunks
-        self._sync_responses_iterator: Any = None
+        self._sync_responses_iterator: Iterator[object] | None = None
 
     def _make_message_start(self) -> dict[str, object]:
         return {
@@ -312,11 +312,9 @@ class AnthropicResponsesStreamWrapper:
             else:
                 if self._sync_responses_iterator is None:
                     self._sync_responses_iterator = iter(self.responses_stream)
+                sync_iterator: Final = self._sync_responses_iterator
                 missing: Final = object()
-                while True:
-                    event = await asyncio.to_thread(next, self._sync_responses_iterator, missing)
-                    if event is missing:
-                        break
+                while (event := await asyncio.to_thread(next, sync_iterator, missing)) is not missing:
                     self._process_event(event)
                     if self._chunk_queue:
                         return self._chunk_queue.popleft()