Update .env.example and enhance create_model function for dual LLM configuration

- Updated .env.example to include new keys for dual LLM configuration, allowing for both general and boost settings.
- Modified create_model function to support an optional use_boost parameter, enabling the selection of either general or boost LLM configurations based on availability.
- Improved logging to indicate which LLM configuration is being used during model creation, enhancing clarity for users.

.env.example

@@ -1,8 +1,12 @@
-# Zep Cloud API Key
-# 从 https://app.getzep.com 获取
-ZEP_API_KEY=
+# ===== ZEP记忆图谱配置 =====
+ZEP_API_KEY=your_zep_api_key_here
 
-# LLM API Key
-LLM_API_KEY=
-LLM_BASE_URL=
-LLM_MODEL_NAME=
+# ===== 通用 LLM 配置 =====
+LLM_API_KEY=your_api_key_here
+LLM_BASE_URL=https://api.openai.com/v1
+LLM_MODEL_NAME=gpt-4o-mini
+
+# ===== 加速 LLM 配置（可选）=====
+LLM_BOOST_API_KEY=your_boost_api_key_here
+LLM_BOOST_BASE_URL=https://another-api-provider.com/v1
+LLM_BOOST_MODEL_NAME=gpt-4o-mini