Argument labels for bit_array.slice and string.slice are inconsistent

```gleam
// bit_array
pub fn slice(
from string: BitArray,
at position: Int,
take length: Int,
) -> Result(BitArray, Nil)

// string
pub fn slice(
from string: String,
at_index idx: Int,
length len: Int,
) -> String
```

It would be nice if they had the same labels. I tried looking for more functions like that, but I didn't find anything else.