[kumo] stabilize Select object-map items

[ftzi]

Issue

Select's documented object-map items form normalizes to a new array on every render, so equivalent parent rerenders can trigger redundant Base UI item-store updates and SelectValue renders.

A focused regression on current main rerendered the documented inline object-map pattern with unchanged entries. React Profiler recorded two commits before the fix—the parent rerender and a Base UI subscriber update—and one afterward. A consumer reproduction also surfaced the redundant updates as React act warnings during async parent rerenders; using a stable array avoided them.

Base UI compares items by identity, while Kumo's Object.entries(...).map(...) normalization changes that identity each render.

Solution

• Reuse the previous normalized object-map array when an ordered, shallow comparison of selection values, labels, and disabled metadata matches.
• Preserve caller-provided array identity and propagate selection value, label, order, and disabled changes.
• Add focused regression tests and a patch changeset for @cloudflare/kumo.

Validation

• pnpm test (52 files, 1,281 tests) and pnpm test:ci (9 tests)
• pnpm format:check, pnpm lint, pnpm typecheck, and pnpm ci:typecheck
• Kumo build and package validation, pnpm lockfile-check, and changeset validation

Limit

Normalization intentionally compares labels with Object.is; a newly created React element used as a label is treated as changed.

AI disclosure

This change and pull request description were prepared by an AI coding agent at the contributor's direction.

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  • Tests included/updated
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