Improve handling of MSRV

[jakoschiko]

Ideas:

• Add a rust-version entry to Cargo.toml
  • Let's add this to the workspace Cargo.toml to reduce redundancy
  • Cargo will use the MSRV in the foreseeable future
• Remove MSRV from CONTRIBUTION.md, this reduces redundancy
• Change the CI so that it reads the MSRV from the workspace Cargo.toml, similar to how release.yml is extracting the version

After these steps there is only a single place that defines the MSRV.

[duesee]

Superseeded by https://github.com/duesee/imap-codec/issues/616

[jakoschiko]

Superseeded by #616

Are you sure? That might cause a stack overflow.

[duesee]

I... uhm... I guess this is what happens when you comment with a flaky Internet connection. No idea what happened.

[jakoschiko]

Relates to #534

[duesee]

cargo read-manifest requires a non-virtual manifest (and is deprecated). We can add it to imap-codec/imap-typess Cargo.toml and read it via ...

cargo metadata --format-version=1 --no-deps | jq -r '.packages[] | select(.name == "imap-codec") | .rust_version

Nit: The rust_version in imap-codec would be used here and the one from imap-types could potentially be different... It's still an improvement.

Nit: We need jq as build dependency and I'm too lazy to document it. WHY CANT EVERYBODY JUST USE nix develop?! Joking :-)

[duesee]

Done in #662.