facet-rs / facet / 20020740731

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feat: make repr(transparent) imply facet(transparent) for single-field tuple structs

When a tuple struct has `#[repr(transparent)]` and exactly 0 or 1 fields,
the facet derive macro will now automatically use transparent semantics,
removing the need to also add `#[facet(transparent)]`.

This aligns with the common use case of newtype wrappers that use
`repr(transparent)` for memory layout optimization - they typically also
want transparent serialization behavior.

Note: For tuple structs with multiple fields (e.g., with PhantomData),
`repr(transparent)` does NOT automatically imply `facet(transparent)` since
facet's transparent semantics only support 0-1 fields. Users must explicitly
add `#[facet(transparent)]` in those cases.

Closes #1172

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