refactor(cli/rustup-mode): avoid redundant allocs in target_add()

[rami3l]

Follow-up on a minor pre-existing issue discovered when reviewing #5042.

This patch avoids an extra .to_string() allocation and a redundant into_iter() -> collect() -> into_iter() round trip.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[djc]

Nice, this seems much better.

The one other thing I played with was adding a Component::std(target) constructor wrapping Component::new("rust-std".to_string(), Some(target), false).

View changes since this review

[rami3l]

The one other thing I played with was adding a Component::std(target) constructor wrapping Component::new("rust-std".to_string(), Some(target), false).

@djc Sounds pretty much like a systematic replacement. I can do this as a follow-up.