add randfile

csst_common/utils/__init__.py

 from ._module_docstr import ModuleHeader
 from ._io import remove_dir, remove_files
+from .tempfile import randfile

csst_common/utils/tempfile.py

+import secrets
+import string
+
+
+def randfile(digits=20, ext=".fits"):
+    """
+
+    Parameters
+    ----------
+    digits
+    ext
+
+    Returns
+    -------
+
+    Examples
+    --------
+    >>> fname = randfile(20)
+    >>> print(fname)
+
+    """
+    # 生成包含大小写字母和数字的字符集
+    characters = string.ascii_letters + string.digits
+    # 使用secrets模块生成指定长度的随机字符串
+    random_string = ''.join(secrets.choice(characters) for _ in range(digits)) + ext
+    return random_string
+