Update Rust version to 1.86

[simongdavies]

Updates Rust Version to 1.86

@syntactically there is a reference to 1.85 here I did not know if this needed to be updated or how?

[dblnz]

LGTM!

[syntactically]

@simongdavies That is there to provide the toolchain used by the dev/verify-msrv.sh script, so if all the msrvs have been updated then it should indeed be replaced by 1.86, otherwise there should be a new 1.86 entry added to have both available. If you don't mind the extra effort, it would be great to replace/add as appropriate:

            "1.86" = {
              date = "2025-04-03";
              channel = "stable";
              sha256 = "sha256-X/4ZBHO3iW0fOenQ3foEvscgAPJYl2abspaBThDOukI=";
            };

[syntactically]

Oh, I just realised you already merged this, I will do it myself and roll it in to my next PR, sorry for the noise.