perf: optimize NonZero negation using bounded integers

[l3ft0ver]

Summary

Optimizes negation for NonZero<T> signed integer types (i8, i16, i32, i64, i128) by using bounded integers directly via NegateHelper, avoiding the generic path through Neg<T>. Addresses the TODO comment on line 88.

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Type of change

Please check one:

• Bug fix (fixes incorrect behavior)
• New feature
• Performance improvement
• Documentation change with concrete technical impact
• Style, wording, formatting, or typo-only change

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are only minor wording, grammar, formatting, or style changes.
Such PRs may be closed without detailed review.

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Why is this change needed?

The current implementation performs unnecessary conversions: unwraps NonZero<T> to T, calls Neg<T>, then converts back. The TODO comment explicitly requests optimization using bounded integers.

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What was the behavior or documentation before?

Generic implementation: NonZero<T> → T → T (via Neg<T>) → NonZero<T>, going through the generic Neg<T> trait.

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What is the behavior or documentation after?

For signed integer types, uses bounded integers directly: NonZero<T> → T → bounded int → NegateHelper::negate() → T → NonZero<T>. Avoids intermediate Neg<T> call. Generic implementation remains for felt252.

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Related issue or discussion (if any)

Addresses TODO comment on line 88: // TODO(orizi): Optimize using bounded integers.

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Additional context

Gated behind bounded-int-utils feature flag, consistent with other bounded integer optimizations. Maintains same behavior and error handling, including minimum value edge cases.

[reviewable-StarkWare]

This change is 

[orizi]

@orizi made 1 comment.
Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @l3ft0ver).

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corelib/src/zeroable.cairo line 98 at r1 (raw file):

    // This uses NegateHelper directly on bounded integers, which is more efficient
    // than the generic implementation that goes through Neg<T>
    #[feature("bounded-int-utils")]

this is much much worse solution from the original implementation with the todo.