bump to 4.8.0-rc1

[AdrienChampion]

I'm starting to use lean-auto, and noticed it does not require std's stable branch but main instead, which does not build as it's now in 4.8.0-rc1.

I have a version of lean-auto that builds on 4.8.0-rc1 here. I don't think you'd want to merge it as is, but hopefully it can be useful as a blueprint for you.

The main things I had to accomodate are:

• std is now batteries (and moved from leanprover to leanprover-community on github);
• simp and other tactics behave slightly differently causing a few proofs to fail, solved by removing/adding minor things;
• theorem-s now have to have type Prop, causing some of your theorems to become (sometimes noncomputable) def-s.

I think that's most of it.

Also, it seems some definitions are still under the Std namespace such as Std.Queue. So it might be a good idea to wait until 4.8.0 releases before updating, and probably require std batteries from its stable branch.

[PratherConid]

@AdrienChampion I've just removed Std from lean-auto's dependencies. It seems that enough definitions/theorems have been moved to leanprover/lean4 such that lean-auto no longer needs to depend on Std. So, the renaming part is no longer necessary.

[PratherConid]

It still makes sense to wait for the stable release.

[dranov]

@PratherConid See #27