Unused import prefixes

[hafihaf123]

Adds a new nursery lint, unused_import_prefixes, which detects and suggests removing redundant crate::... prefixes in use statements when importing items that are descendants of the current module.

Fixes #17084

• Followed lint naming conventions
• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation
• Run cargo dev fmt

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changelog: new lint: [unused_import_prefixes]

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @dswij (or someone else) some time within the next two weeks.

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: 8 candidates
• 8 candidates expanded to 8 candidates
• Random selection from Jarcho, dswij, llogiq, samueltardieu

[github-actions]

Lintcheck changes for 473b125

Lint	Added	Removed	Changed
clippy::unused_import_prefixes	53	0	0

This comment will be updated if you push new changes

[rustbot]

This PR was rebased onto a different master 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.