Support timeout values in client::register() and client::authenticate()

[Brisk4t]

Implements #65.

Not sure how much we care to keep tokio optional but guarded it just in case. I doubt there are any no_std implementations of this since both authenticate() and register() functions are async by default.

Note on updated rust-toolchain file:

I changed 1.85.1 to stable since i was getting version errors with icu_* and idna_adapter while building with the existing 1.85.1 but if we need to keep it pinned I could just make it 1.86 (which is the lowest supported version for those two crates), builds fine with stable though 🤷

[Brisk4t]

Updated the CI and crate toolchain version to 1.86.0 which is the minimum required version for crate deps failing in the build.

@Progdrasil I can make this a different PR in case you want to merge just the CI updates without the workflow checks since it will fail those until the toolchain update applies.

[Progdrasil]

@iinuwa is this change okay on your side?

[iinuwa]

yeah, that's fine, we're at 1.94

[Brisk4t]

Do we wanna bump the version all the way to 1.94 then? Or do we want to stick to minimal functional updates?

[Progdrasil]

Updated the CI and crate toolchain version to 1.86.0 which is the minimum required version for crate deps failing in the build.

@Progdrasil I can make this a different PR in case you want to merge just the CI updates without the workflow checks since it will fail those until the toolchain update applies.

Having it in this PR is fine for me, I just want to make sure this doesn't break for others downstream.