New lint: empty_expect

[konard]

Summary

• Adds new empty_expect lint (category: suspicious)
• Detects .expect("") calls with empty string message
• These provide no more context than .unwrap() and are sometimes used to bypass unwrap_used

Test plan

• Added UI tests for Option::expect("") and Result::expect("")
• Verified non-empty .expect("msg") does not trigger

Closes #16764

🤖 Generated with Claude Code

[rustbot]

r? @llogiq

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The reviewer was selected based on:

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[rustbot]

⚠️ Warning ⚠️

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  • 6373de8

[github-actions]

Lintcheck changes for 6373de8

Lint	Added	Removed	Changed
clippy::empty_expect	1	0	0

This comment will be updated if you push new changes

[rustbot]

☔ The latest upstream changes (possibly #16687) made this pull request unmergeable. Please resolve the merge conflicts.