Fix Zod v4 async function type inference in schema definitions - #458

Zod v4's z.function() with z.promise() output incorrectly infers MaybeAsync<T> (union of T | Promise<T>) instead of Promise<T>, causing TypeScript errors in plugin and event handler schemas:

// Before: Type error - MaybeAsync<void> not assignable to Promise<void>
storage: z.object({
  set: z.function({
    input: z.tuple([]).rest(z.any()),
    output: z.promise(z.void())  // Infers as () => void | Promise<void>
  }),
})

// After: Correct async inference
storage: z.object({
  set: createAsyncFunctionSchema(
    z.function({
      input: z.tuple([]).rest(z.any()),
      output: z.promise(z.void())  // Infers as () => Promise<void>
    })
  ),
})

Changes

• Added createAsyncFunctionSchema helper in shared/zod-helpers.ts that wraps function schemas with z.custom<> to leverage Zod v4's implementAsync type parameter for correct Promise inference

• Updated async function definitions in:

  • system/plugin.zod.ts: Plugin lifecycle hooks and storage methods
  • system/events.zod.ts: Event handler functions
  • system/job.zod.ts: Job handler functions

See: colinhacks/zod#4143

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