Align rust version with CI image's Rust version

[rosarp]

Current CI Image is paritytech/ci-unified:bullseye-1.81.0-2024-09-11-v202409111034

This also helps with Cargo.lock version issue:

• [encointer] introduce swap options for businesses through democracy polkadot-fellows/runtimes#541 (comment)
• Bump polkadot-sdk #3104 (comment)

Version of rust < 1.83 uses version "3" in Cargo.lock while version >= 1.83 uses version "4" in Cargo.lock.
This PR also solves this issue while keeping aligned with rust version used in github CI image. Which will eliminate back-and-forth build failures caused due to rust version mismatches.

[bkontur]

why do we need rust-analyzer?

[rosarp]

rust-analyzer is not downloaded for any other version by default.
If this settings is not enabled, rust-analyzer wont work locally, as editor will try to load rust-analyzer for currently enabled rust version (if configured to use it).

Those who need it locally will need to run this command once in this repository:

rustup component add rust-analyzer

So, if larger population of devs dont need rust-analyzer locally, I can remove it.

[bkontur]

hmm, I think I have never used rustup component add rust-analyzer, so now I think more we should not push local settings/setups to the git

[rosarp]

This is only applicable if you are using version other than stable.
Even for nightly it will be required locally.
I will remove both component from this config, as both will be only required on local.
Only that, every developer working on this repository will need to add this line to satisfy IDE.

[rosarp]

hmm, I think I have never used rustup component add rust-analyzer, so now I think more we should not push local settings/setups to the git

After thinking a bit, setting channel is also required for local setting only. as github CI, takes care of the version for git build.
So, basically these settings will help user with consistent build experience. What happens on CI can be reproduced locally.

[serban300]

I would also remove rust-analyzer from here if it's not needed in the CI. And I think we need to add rustfmt and clippy.

Also, to ensure that the CI image uses the same version as the one provided in our rust-toolchain.toml override, I think it would be good to have a test that checks if they are the same. We can get the override with rustup show active-toolchain |& tail -n 1 | cut -d " " -f1 and the CI default with rustup default | cut -d " " -f1