Investigate PlackettLuce ties

[philihp]

vivekjoshy/openskill.py#176 demonstrates a bug that manifests from ties. Investigate this and see if the javascript library is impacted. I believe I handled this with the line

https://github.com/philihp/openskill.js/blob/main/src/models/plackett-luce.ts#L17

However I should be sure by verifying it against tests