refactor(global_var): 重构全局变量管理并添加工作目录功能

- 添加 _workdir 全局变量以存储工作目录路径
- 在 init_global_var 函数中初始化 _workdir
- 新增 get_workdir 函数以获取工作目录路径
- 调整全局变量的定义和初始化顺序

global_var.py

@@ -5,14 +5,19 @@ _prompt_store = None
 _sql_engine = None
 _docs = None
 _datasets = None
-
+_model = None
+_tokenizer = None
+_workdir = None
 def init_global_var(workdir="workdir"):
-    """Initialize all global variables"""
     global _prompt_store, _sql_engine, _docs, _datasets
     _prompt_store = get_prompt_tinydb(workdir)
     _sql_engine = get_sqlite_engine(workdir)
     _docs = scan_docs_directory(workdir)
     _datasets = get_all_dataset(workdir)
+    _workdir = workdir
+
+def get_workdir():
+    return _workdir
 
 def get_prompt_store():
     return _prompt_store
@@ -42,9 +47,6 @@ def set_datasets(new_datasets):
     global _datasets
     _datasets = new_datasets
 
-_model = None
-_tokenizer = None
-
 def get_model():
     return _model