Need rust-toolchain about zkevm-circuits

[CPerezz]

Seems fine to me! We discussed this with @han0110 and @ChihChengLiang and agreed to setup the toolchain file targeting stable and not overriting it in the CI!

[han0110]

I think right now we don't use features requiring nightly? For the stable version we are using 1.53 (stick to CI). Does the warning can't set wrap_comments = true from cargo fmt leads you think we are using nightly?

[Lawliet-Chan]

Actually, I met a bug when I first built the code because of my old nightly version and I update rustc to fix it.

Maybe our codes don't need nightly, but we cannot guarantee the dependent libs don't have it. Sometimes some library requires a specific version of nightly.
So a unified version is more conducive to the standardization of the project. rust-toolchain can constrain and unify the version of nightly. It is friendly to developers.