fix(non_zero_suggestions): don't lint signed integer div/rem as NonZero

[Lfan-ke]

Summary

Fixes #17382.

Div<NonZero<T>> and Rem<NonZero<T>> are only implemented for unsigned integer types in std. The lint was suggesting NonZeroI*::from(x) as the RHS of / or % when the divisor was derived from a signed NonZero type, which produces code that fails to compile:

let s: i64 = 10;
let t = NonZeroI32::new(3).unwrap();

// Before fix: lint fires and auto-fixes to:
let quotient = s / NonZeroI64::from(t); // error: i64 / NonZeroI64 not implemented

Root Cause

In check_expr, the Div | Rem branch called check_non_zero_conversion unconditionally. The get_target_non_zero_type function returned NonZeroI* for signed types too, but the corresponding arithmetic impls do not exist in std.

Fix

Guard the div/rem path: only call check_non_zero_conversion when the RHS type is ty::Uint(_). Signed types still benefit from the lint in non-div/rem contexts (e.g., plain let x: i64 = i64::from(nz.get()) → NonZeroI64::from(nz)).

Test Plan

• Added negative test cases for i64 / i64::from(nz.get()) and i64 % i64::from(nz.get()) to tests/ui/non_zero_suggestions.rs - these must NOT trigger the lint.
• Existing positive test cases for unsigned types remain unchanged.

changelog: [non_zero_suggestions] Fix false positive when suggesting NonZero for signed integer div/rem

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