docs(immer): fix setPerson updater type in usage examples

[TheSeydiCharyyev]

The setPerson action type in both usage examples of immer.md is malformed — a misplaced parenthesis puts | PersonStoreState['person'] inside the function's return type instead of making it a top-level union member.

Current:

setPerson: (
  nextPerson: (
    person: PersonStoreState['person'],
  ) => PersonStoreState['person'] | PersonStoreState['person'],
) => void

This types nextPerson as (person: P) => (P | P) — i.e. always a function, with a redundant P | P return type. But the example's own implementation handles both a value and an updater function:

setPerson: (nextPerson) =>
  set((state) => ({
    person:
      typeof nextPerson === 'function'
        ? nextPerson(state.person)
        : nextPerson,
  })),

With the current type the : nextPerson branch is unreachable.

The intended type is a value-or-updater union — the same pattern already used correctly by setAge in create.md:

nextAge:
  | AgeStoreState['age']
  | ((currentAge: AgeStoreState['age']) => AgeStoreState['age']),

Diff

  setPerson: (
-   nextPerson: (
-     person: PersonStoreState['person'],
-   ) => PersonStoreState['person'] | PersonStoreState['person'],
+   nextPerson:
+     | PersonStoreState['person']
+     | ((person: PersonStoreState['person']) => PersonStoreState['person']),
  ) => void

Applied to both usage examples (the plain createStore example and the immer example). Docs-only change — no changeset needed.

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Project	Deployment	Actions	Updated (UTC)
zustand-demo	Ready	Preview, Comment	May 20, 2026 10:08am

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commit: 9907854