Optimizations and bug fixes for v0.2.1

[LuisFerLCC]

Implement the following optimizations and bug fixes for 0.2.1:

• Move #[allow(single_use_lifetimes)] in both impl Display for T and impl Error for T above user-provided attributes to avoid overriding them
• Allow structs with at least one field with type never (!) to ignore the display attribute, as such a struct is itself not constructible
• Fully qualify the path for the unreachable macro

[Copilot]

Pull request overview

This PR implements three optimizations and bug fixes for version 0.2.1, focusing on attribute ordering, handling never-type structs, and macro path qualification.

Key changes:

• Repositioned #[allow(single_use_lifetimes)] above user attributes to prevent overriding user-provided attributes
• Added support for structs with never (!) type fields to be treated as empty types, not requiring a display attribute
• Fully qualified the unreachable! macro path and renamed EmptyEnum to EmptyType for consistency

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/src/structs.rs	Updated comment from FIXME to TODO regarding redundant_lifetimes expectation placement
tests/src/enums.rs	Corrected comment to reference Tuple variant instead of TupleVariant for consistency
tests/src/enum_variants.rs	Renamed enum variants for consistency (UnitVariant → Unit, NamedFieldVariant → NamedFields, TupleVariant → Tuple) and removed completed TODO
impl/src/types/mod.rs	Moved #[allow(single_use_lifetimes)] above user attributes in both Display and Error impl blocks, updated test expectations
impl/src/types/fmt/mod.rs	Added never type detection for structs, renamed EmptyEnum to EmptyType, fully qualified unreachable macro, added test for never-type struct

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