Add auto-walrus pre-commit hook

[anayden]

Hey @AntonPetrov I stumbled upon this pre-commit hook and immediately realized R2DT is in a dire need of it.

[github-actions]

Docker image tag(s) pushed:

rnacentral/r2dt:pr-126

Labels added to images:

org.opencontainers.image.created=2023-11-22T20:29:35.850Z
org.opencontainers.image.description=Visualise RNA secondary structure in consistent, reproducible and recognisable layouts
org.opencontainers.image.licenses=Apache-2.0
org.opencontainers.image.revision=a5e96b6c437ec611060b0f47f537a126d91959ec
org.opencontainers.image.source=https://github.com/RNAcentral/R2DT
org.opencontainers.image.title=R2DT
org.opencontainers.image.url=https://github.com/RNAcentral/R2DT
org.opencontainers.image.version=pr-126

[AntonPetrov]

@anayden What a really useful contribution, thank you very much! 🦭🦭🦭

Just curious if it actually changes any existing code when you do pre-commit run auto-walrus? If it does, those changes should probably be made in the same PR (after all the tests pass of course).

[anayden]

Just curious if it actually changes any existing code

No, it doesn't. The code is already 100% walrus'ed. But this is a nice-to-have hook for future contributions.
It just makes syntax more modern (and more walrus-ish), where applicable.