Unexpected behavior when arg is input as a string or literally same integer

```python
@ring.dict({})
def f(a):
    print("not using cache")
    return str(a)
f(1)
f.storage.backend
f("1")
f.storage.backend
```
The output is shown as below:
not using cache
'1'
{'__main__.f:1': '1'}
'1'
{'__main__.f:1': '1'}