refactor(usage): 统一 cache token 提取逻辑，新增请求缓存指纹记录

- 新增 extract_cache_read_tokens() 兼容 OpenAI/Claude/Gemini 多种字段命名
- parsers/stream_processor/cli_event_mixin 统一使用提取函数替换内联逻辑
- 同时兼容 prompt_tokens/completion_tokens (OpenAI) 和 input_tokens/output_tokens (Claude)
- 新增 cache_fingerprint 模块，在 telemetry 记录时自动计算并附带请求缓存指纹
- 新增对应单元测试

tests/api/handlers/base/test_openai_usage_parsing.py

@@ -0,0 +1,113 @@
+from __future__ import annotations
+
+from typing import Any
+
+from src.api.handlers.base.parsers import OpenAICliResponseParser, OpenAIResponseParser
+from src.api.handlers.base.response_parser import (
+    ParsedChunk,
+    ParsedResponse,
+    ResponseParser,
+    StreamStats,
+)
+from src.api.handlers.base.stream_context import StreamContext
+from src.api.handlers.base.stream_processor import StreamProcessor
+
+
+class _DummyParser(ResponseParser):
+    def parse_sse_line(self, line: str, stats: StreamStats) -> ParsedChunk | None:
+        return None
+
+    def parse_response(self, response: dict[str, Any], status_code: int) -> ParsedResponse:
+        return ParsedResponse(raw_response=response, status_code=status_code)
+
+    def extract_usage_from_response(self, response: dict[str, Any]) -> dict[str, int]:
+        return {}
+
+    def extract_text_content(self, response: dict[str, Any]) -> str:
+        return ""
+
+
+def test_openai_response_parser_extracts_cached_tokens_from_prompt_tokens_details() -> None:
+    parser = OpenAIResponseParser()
+
+    usage = parser.extract_usage_from_response(
+        {
+            "usage": {
+                "prompt_tokens": 120,
+                "completion_tokens": 18,
+                "prompt_tokens_details": {"cached_tokens": 96},
+            }
+        }
+    )
+
+    assert usage["input_tokens"] == 120
+    assert usage["output_tokens"] == 18
+    assert usage["cache_read_tokens"] == 96
+
+
+def test_openai_cli_response_parser_extracts_cached_tokens_from_input_tokens_details() -> None:
+    parser = OpenAICliResponseParser()
+
+    usage = parser.extract_usage_from_response(
+        {
+            "type": "response.completed",
+            "response": {
+                "usage": {
+                    "input_tokens": 2048,
+                    "output_tokens": 128,
+                    "input_tokens_details": {"cached_tokens": 1792},
+                }
+            },
+        }
+    )
+
+    assert usage["input_tokens"] == 2048
+    assert usage["output_tokens"] == 128
+    assert usage["cache_read_tokens"] == 1792
+
+
+def test_stream_processor_extracts_cached_tokens_from_openai_cli_converted_event() -> None:
+    processor = StreamProcessor(request_id="req_test", default_parser=_DummyParser())
+    ctx = StreamContext(model="gpt-5", api_format="openai:chat")
+
+    processor._extract_usage_from_converted_event(
+        ctx,
+        {
+            "type": "response.completed",
+            "response": {
+                "usage": {
+                    "input_tokens": 4096,
+                    "output_tokens": 64,
+                    "input_tokens_details": {"cached_tokens": 3584},
+                }
+            },
+        },
+        "response.completed",
+    )
+
+    assert ctx.input_tokens == 4096
+    assert ctx.output_tokens == 64
+    assert ctx.cached_tokens == 3584
+
+
+def test_stream_processor_extracts_cached_tokens_from_openai_chat_converted_event() -> None:
+    processor = StreamProcessor(request_id="req_test", default_parser=_DummyParser())
+    ctx = StreamContext(model="gpt-5", api_format="openai:chat")
+
+    processor._extract_usage_from_converted_event(
+        ctx,
+        {
+            "object": "chat.completion.chunk",
+            "choices": [],
+            "usage": {
+                "prompt_tokens": 512,
+                "completion_tokens": 21,
+                "prompt_tokens_details": {"cached_tokens": 480},
+            },
+        },
+        "chat.completion.chunk",
+    )
+
+    assert ctx.input_tokens == 512
+    assert ctx.output_tokens == 21
+    assert ctx.cached_tokens == 480