fix: convert the uint64's from some backends' hash() to the desired int64

[NickCrews]

fixes https://github.com/ibis-project/ibis/issues/9135

I don't love the logic that does the conversion. It seems more complicated than it needs to be, and I don't like how I had to implement it once for each backend, but maybe there is no universal way to do this. If you can think of a cleaner way to do this or sidestep the need entirely that would be awesome

[gforsyth]

Hey @NickCrews -- I think the exasol failure is fixed on main if you want to rebase this

[NickCrews]

hey @gforsyth can you give this a review when you get the chance? Thanks!

[NickCrews]

@jcrist you all do the rebase and merge, right? Not squash?

[jcrist]

Depends on the commits and the desired changelog entries (multiple user facing changes would need multiple commits to note). Since this is only 1 commit and change, either works tbh.