feat: 将 StreamOptimizer 参数改为可配置

将 StreamOptimizer 中的硬编码参数改为通过配置文件可配置的参数，提高了系统的灵活性。具体修改包括：

在 .env.example 中添加 stream_optimizer 相关配置参数
在 app/core/config.py 中添加对应的配置项
修改 app/services/chat/stream_optimizer.py 从配置中读取参数
在 README.md 中添加流式输出优化配置的详细说明

app/core/config.py

@@ -17,6 +17,13 @@ class Settings(BaseSettings):
     UPLOAD_PROVIDER: str = "smms"
     SMMS_SECRET_TOKEN: str = ""
     TEST_MODEL: str = "gemini-1.5-flash"
+    
+    # 流式输出优化器配置
+    STREAM_MIN_DELAY: float = 0.016
+    STREAM_MAX_DELAY: float = 0.024
+    STREAM_SHORT_TEXT_THRESHOLD: int = 10
+    STREAM_LONG_TEXT_THRESHOLD: int = 50
+    STREAM_CHUNK_SIZE: int = 5
 
     def __init__(self):
         super().__init__()

app/services/chat/stream_optimizer.py

@@ -4,6 +4,7 @@ import asyncio
 import math
 from typing import Any, List, AsyncGenerator, Callable
 from app.core.logger import get_openai_logger, get_gemini_logger
+from app.core.config import settings
 
 logger_openai = get_openai_logger()
 logger_gemini = get_gemini_logger()
@@ -112,5 +113,20 @@ class StreamOptimizer:
 
 
 # 创建默认的优化器实例，可以直接导入使用
-openai_optimizer = StreamOptimizer(logger=logger_openai)
-gemini_optimizer = StreamOptimizer(logger=logger_gemini)
+openai_optimizer = StreamOptimizer(
+    logger=logger_openai,
+    min_delay=settings.STREAM_MIN_DELAY,
+    max_delay=settings.STREAM_MAX_DELAY,
+    short_text_threshold=settings.STREAM_SHORT_TEXT_THRESHOLD,
+    long_text_threshold=settings.STREAM_LONG_TEXT_THRESHOLD,
+    chunk_size=settings.STREAM_CHUNK_SIZE
+)
+
+gemini_optimizer = StreamOptimizer(
+    logger=logger_gemini,
+    min_delay=settings.STREAM_MIN_DELAY,
+    max_delay=settings.STREAM_MAX_DELAY,
+    short_text_threshold=settings.STREAM_SHORT_TEXT_THRESHOLD,
+    long_text_threshold=settings.STREAM_LONG_TEXT_THRESHOLD,
+    chunk_size=settings.STREAM_CHUNK_SIZE
+)