fix(versioning): Preserve optionality changed from its declaration

[Timothee Guerin (timotheeguerin)]

An optionality transformation can leave copied properties carrying versioning history that no longer describes them. This causes OptionalProperties<T> to reject @madeRequired properties, and spreading the result can make those properties required again in version snapshots.

This is the simple declaration-comparison alternative for #11592, independent of the structural-override prototype in #11969. These are alternatives, not stacked changes.

Versioning compares property.optional with property.node.optional. When they differ, it skips optionality diagnostics and preserves the transformed optionality when computing snapshots from the original graph. There is no helper-name special case, provenance tracking, extra state, or change to metadata getters.

model Source {
  @madeRequired(Versions.v2)
  foo: string;
}

model Patch {
  ...OptionalProperties<Source>;
}

Source.foo retains its version history; Patch.foo stays optional in every version. Property addition, removal, rename, and type history remain intact. Invalid optionality annotations on unchanged original declarations still diagnose.

Limitations: same-value transforms and transforms that restore the declared optionality are undetectable. New optionality augments on transformed copies are ignored for validation and snapshots too, because this rule cannot distinguish them from inherited annotations. Properties without a model-property declaration node cannot be identified as transformed. This draft intentionally demonstrates a bounded heuristic rather than a general transformation contract.

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/versioning@11968

commit: 823e7f0

[github-actions]

All changed packages have been documented.

• ✅ @typespec/versioning

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@typespec/versioning - fix ✏️

Preserve transformed property optionality in version snapshots and skip incompatible optionality diagnostics when the property differs from its original declaration, without special-casing transformation helpers.

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