deprecate React 19 helpers

[okyrychenko-dev]

Summary

Deprecate the generic React 19 helper wrappers while preserving compatibility and guiding consumers toward direct composition of supported React primitives.

Changes

• Mark createTransitionAction, useActionStateAdapter, and useOptimisticReducer deprecated in their public declarations.
• Document direct migrations to startTransition, useActionState, and useOptimistic.
• Explain asynchronous transition lifetime, latest-action behavior, and optimistic transition dispatch requirements.
• Preserve the existing runtime implementations, root exports, and characterization coverage.
• Record why equivalent shallow wrappers should not be reintroduced.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-18T20:05:12.489015Z	34ea976	PR opened

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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