chore(lint): satisfy stable/1.86.x's stricter formatters on backported code

stable/1.86.x enforces PLR0915 in the main ruff config; internal staging
moved it to a separate strict gate, so two functions that ship cleanly on
staging trip it here: _build_usage_only_response_from_chunks (#31035) and
the post-call cost callback (#30788). Exempt both files via the existing
per-file-ignores convention rather than editing the picked source. Also
black-normalize blank lines around the reconstructed TestInterruptedStream
class in the #30787 test file.

ruff.toml

@@ -19,3 +19,5 @@ exclude = ["litellm/types/*", "litellm/__init__.py", "litellm/proxy/example_conf
 "litellm/responses/streaming_iterator.py" = ["PLR0915"]
 "litellm/files/main.py" = ["PLR0915"]
 "litellm/llms/litellm_proxy/skills/sandbox_executor.py" = ["PLR0915"]
+"litellm/proxy/hooks/proxy_track_cost_callback.py" = ["PLR0915"]
+"litellm/proxy/pass_through_endpoints/llm_provider_handlers/anthropic_passthrough_logging_handler.py" = ["PLR0915"]

tests/test_litellm/proxy/pass_through_endpoints/llm_provider_handlers/test_anthropic_passthrough_logging_handler.py

@@ -752,6 +752,8 @@ class TestBuildCompleteStreamingResponseRobustness:
         result = self._build(chunks)
         assert result is not None
         assert result.choices[0].message.content == "The stream ends with [DONE]"
+
+
 class TestInterruptedStreamOutputTokenRecovery:
     """
     When an Anthropic pass-through stream is interrupted (client disconnect)
@@ -893,7 +895,6 @@ class TestInterruptedStreamOutputTokenRecovery:
         assert usage.completion_tokens == final
 
 
-
 class TestStreamFalseDeduplication:
     """
     Regression tests for the duplicate-callback bug where a streaming pass-through