Feature: Support rustup toolchains

[reneleonhardt]

Is your feature request related to a problem?

Each rustup toolchain is quite big, if you're using cargo-msrv to determine the minimum you'll end up having installed dozens of toolchains.

Describe the solution you'd like

Outdated toolchains should be removed (if the user configures a minimum date or version).

Describe alternatives you've considered

Listing and removing them manually one by one takes a lot of time.

Additional Context

Default directory $HOME/.rustup/toolchains

ls -1 "$(rustup show home)/toolchains"

$ rustup toolchain list
stable-aarch64-apple-darwin (active, default)
nightly-aarch64-apple-darwin
nightly-2024-04-03-aarch64-apple-darwin
nightly-2025-02-01-aarch64-apple-darwin
1.56-aarch64-apple-darwin
1.57.0-aarch64-apple-darwin
1.58.1-aarch64-apple-darwin
1.60-aarch64-apple-darwin
1.60.0-aarch64-apple-darwin
...
1.89.0-aarch64-apple-darwin