add scanl1 to Clash prelude

[vmchale]

This adds scanl1 for vectors.

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[vmchale]

btw what should I tag this branch with so that it works correctly?

[martijnbastiaan]

Overall LGTM

[martijnbastiaan]

btw what should I tag this branch with so that it works correctly?

Everything should just work. But I think GitLab status reporting has been broken for a few days now, I'll look into it tomorrow morning. I think it's to do with the new-style GitHub tokens..

[martijnbastiaan]

CI has been fixed; I've squashed all your commits to make a force push that triggers CI.

[DigitalBrains1]

We usually also add a GitHub PR link or issue link to the Changelog, but it doesn't seem to really add interesting information here, so I suppose it's not a problem that it is not there.

[martijnbastiaan]

I wrote a script that acts like git blame, but instead it shows the PR. But yeah, would be handy-dandy if it was already in the changelog of course.