refactor(config): 移除废弃的数据库配置模块

旧的数据库配置模块 `src/common/database/config` 已被完全移除。该模块已被标记为废弃，其功能已统一整合到 `global_config` 中。

本次重构旨在：
- 简化代码库，消除冗余和过时的文件。
- 统一配置管理，提高可维护性。

此外，对 `AttentionOptimizer` 中的类变量添加了 `ClassVar` 类型注解，以增强代码的清晰度和类型安全性。

src/common/database/config/__init__.py

@@ -1,11 +0,0 @@
-"""数据库配置层
-
-职责：
-- 数据库配置现已集成到全局配置中
-- 通过 src.config.config.global_config.database 访问
-- 优化参数配置
-
-注意：此模块已废弃，配置已迁移到 global_config
-"""
-
-__all__ = []

src/common/database/config/old/database_config.py

@@ -1,149 +0,0 @@
-"""数据库配置管理
-
-统一管理数据库连接配置
-"""
-
-import os
-from dataclasses import dataclass
-from typing import Any
-from urllib.parse import quote_plus
-
-from src.common.logger import get_logger
-
-logger = get_logger("database_config")
-
-
-@dataclass
-class DatabaseConfig:
-    """数据库配置"""
-
-    # 基础配置
-    db_type: str  # "sqlite" 或 "mysql"
-    url: str  # 数据库连接URL
-
-    # 引擎配置
-    engine_kwargs: dict[str, Any]
-
-    # SQLite特定配置
-    sqlite_path: str | None = None
-
-    # MySQL特定配置
-    mysql_host: str | None = None
-    mysql_port: int | None = None
-    mysql_user: str | None = None
-    mysql_password: str | None = None
-    mysql_database: str | None = None
-    mysql_charset: str = "utf8mb4"
-    mysql_unix_socket: str | None = None
-
-
-_database_config: DatabaseConfig | None = None
-
-
-def get_database_config() -> DatabaseConfig:
-    """获取数据库配置
-
-    从全局配置中读取数据库设置并构建配置对象
-    """
-    global _database_config
-
-    if _database_config is not None:
-        return _database_config
-
-    from src.config.config import global_config
-
-    config = global_config.database
-
-    # 构建数据库URL
-    if config.database_type == "mysql":
-        # MySQL配置
-        encoded_user = quote_plus(config.mysql_user)
-        encoded_password = quote_plus(config.mysql_password)
-
-        if config.mysql_unix_socket:
-            # Unix socket连接
-            encoded_socket = quote_plus(config.mysql_unix_socket)
-            url = (
-                f"mysql+aiomysql://{encoded_user}:{encoded_password}"
-                f"@/{config.mysql_database}"
-                f"?unix_socket={encoded_socket}&charset={config.mysql_charset}"
-            )
-        else:
-            # TCP连接
-            url = (
-                f"mysql+aiomysql://{encoded_user}:{encoded_password}"
-                f"@{config.mysql_host}:{config.mysql_port}/{config.mysql_database}"
-                f"?charset={config.mysql_charset}"
-            )
-
-        engine_kwargs = {
-            "echo": False,
-            "future": True,
-            "pool_size": config.connection_pool_size,
-            "max_overflow": config.connection_pool_size * 2,
-            "pool_timeout": config.connection_timeout,
-            "pool_recycle": 3600,
-            "pool_pre_ping": True,
-            "connect_args": {
-                "autocommit": config.mysql_autocommit,
-                "charset": config.mysql_charset,
-                "connect_timeout": config.connection_timeout,
-            },
-        }
-
-        _database_config = DatabaseConfig(
-            db_type="mysql",
-            url=url,
-            engine_kwargs=engine_kwargs,
-            mysql_host=config.mysql_host,
-            mysql_port=config.mysql_port,
-            mysql_user=config.mysql_user,
-            mysql_password=config.mysql_password,
-            mysql_database=config.mysql_database,
-            mysql_charset=config.mysql_charset,
-            mysql_unix_socket=config.mysql_unix_socket,
-        )
-
-        logger.info(
-            f"MySQL配置已加载: "
-            f"{config.mysql_user}@{config.mysql_host}:{config.mysql_port}/{config.mysql_database}"
-        )
-
-    else:
-        # SQLite配置
-        if not os.path.isabs(config.sqlite_path):
-            ROOT_PATH = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "..", "..", ".."))
-            db_path = os.path.join(ROOT_PATH, config.sqlite_path)
-        else:
-            db_path = config.sqlite_path
-
-        # 确保数据库目录存在
-        os.makedirs(os.path.dirname(db_path), exist_ok=True)
-
-        url = f"sqlite+aiosqlite:///{db_path}"
-
-        engine_kwargs = {
-            "echo": False,
-            "future": True,
-            "connect_args": {
-                "check_same_thread": False,
-                "timeout": 60,
-            },
-        }
-
-        _database_config = DatabaseConfig(
-            db_type="sqlite",
-            url=url,
-            engine_kwargs=engine_kwargs,
-            sqlite_path=db_path,
-        )
-
-        logger.info(f"SQLite配置已加载: {db_path}")
-
-    return _database_config
-
-
-def reset_database_config():
-    """重置数据库配置（用于测试）"""
-    global _database_config
-    _database_config = None