feat: update chainfile dependency, return score

[jsstevenson]

close #75

• update to latest chainfile crate release (cheers @claymcleod)
• for the sake of drop-in comparability to pyliftover, add the segment score metric for the liftover to the returned object
• some veeeery tiny optimizations relating to casting between strings and ints
• update the speed test notebook just for kicks. I think it's okay to have this part be kinda unmaintained but I wanted to run it for kicks
• bump to version 0.2.1

[claymcleod]

That's looking great! Thanks for updating the notebook!

[korikuzma]

🚀