Update safetensors_file.py to support context manager protocol

Add __enter__ and __exit__ to allow `with SafeTensorsFile.open_file(tensorsfile, quiet=True) as s:` syntax

safetensors_file.py

@@ -31,6 +31,14 @@ def __init__(self):
 
     def __del__(self):
         self.close_file()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        if self.f is not None:
+            self.f.close()
+
 
     def close_file(self):
         if self.f is not None: