Replace range parsing logic with a 3rd party library

Looks like `ranges` will do this out of the box:

```python
from ranges import Range

# Convert list to ranges
nums = [1, 2, 3, 5, 7, 8, 9, 12]
r = Range(*nums)
print(r)  # Range(1, 4) + Range(5, 6) + Range(7, 10) + Range(12, 13)

# Convert back to list
list(r)  # [1, 2, 3, 5, 7, 8, 9, 12]

# String representation
str(r)  # "1-3,5,7-9,12"
```