Update SLEAP tutorial to work with >=v1.5

[niksirbi]

See https://docs.sleap.ai/latest/whats-new/ and SLEAP v1.5.0 release notes.
Versions >=1.5 include a Pytorch backend and we should switch to teaching that.

We should complete this task latest by August 2026 in time for the next open software summer school.

[niksirbi]

@lochhh, I think that reviewing neuroinformatics-unit/HowTo#81 may help you in tackling this issue, so I recommend doing that first.

While working on that PR, I went through the new SLEAP tutorial, which is very nice.

We should consider more tightly aligning our tutorial to SLEAP's own. We could, in principle, just give SLEAP's official tutorial, but I think there's still value in maintaining our own version of it, to keep some control over what content we teach and how much (depending on available time, per course).

We should also think about whether we should just use the tutorial data SLEAP provides now. But keep in mind that it's a video of two identical black mice, so we can't use an appearance-based model with that. Maybe it's worth sticking to our CalMS21 dataset, which you have already nicely curated. We may be even able to use the same data for the behaviour classification part #16.