[transmute] Remove some SizeEq impls

[joshlf]

Replace calls to Ptr::transmute with calls to transmute_with, which
accepts a CastExact parameter to specify the cast at the call site.

---

• 　 Permit shrinking transmutes in transmute machinery #2912
• 　 [transmute] Encode cast in TryTransmuteFromPtr params #2921
• 　 Replace unsafe_with_size_eq! with transmute_with #2923
• 👉 [transmute] Remove some SizeEq impls #2922
• 　 [transmute] Remove SizeEq super-trait bound #2920

Latest Update: v4 — Compare vs v3

📚 Full Patch History

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Version	v3	v2	v1	Base
v4	vs v3	vs v2	vs v1	vs Base
v3		vs v2	vs v1	vs Base
v2			vs v1	vs Base
v1				vs Base

[gemini-code-assist]

Summary of Changes

Hello @joshlf, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the type casting mechanism within the transmute crate by moving from an implicit Ptr::transmute to a more explicit transmute_with method. This change enhances clarity and type safety by requiring developers to specify the exact casting behavior (sized or unsized) at the point of use. Concurrently, it simplifies the codebase by removing several SizeEq trait implementations and the macro previously used to define them, indicating a consolidation or re-evaluation of how type size equality is managed.

Highlights

• Explicit Type Casting: Replaced calls to the generic Ptr::transmute method with transmute_with, which explicitly accepts CastSizedExact or CastUnsized parameters to specify the casting behavior at the call site.
• Removal of SizeEq Implementations: Removed several explicit impl_size_eq! macro calls for fundamental types such as bool, char, str, and NonZero variants, streamlining the type system's handling of size equality.
• Macro Refactoring: The impl_size_eq! macro definition itself was removed from src/util/macros.rs, indicating a shift away from its usage for defining SizeEq traits.
• New Cast Type Imports: Imported CastUnsized and CastSizedExact from crate::pointer::cast to support the new explicit casting mechanism.

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[gemini-code-assist]

Code Review

This pull request is a good refactoring. It replaces the impl_size_eq! macro with more explicit calls to transmute_with, specifying the cast type directly. This improves code clarity and maintainability. The changes are applied consistently, and the correct cast types (CastSizedExact and CastUnsized) are used where appropriate. I see no issues with this change.