Signature of decorated function is not type checked by mypy

The following has mypy  (expectedly) failing with `error: Argument 1 to "f1" has incompatible type "int"; expected "str"  [arg-type]`

```python
async def f1(x: str, y: int) -> str:
    return x + str(y)


async def main():
    await f1(1, 1)
```

But decorating `f1` with `@alru_cache` prevents mypy from detecting any issue.