[EnityAdapter] setMany creates duplicated IDs for entities with the same ID

[demyanm]

Related to #5096 and #4890.

When using the sorted state adapter, calling setMany with multiple entities sharing the same id results in duplicated IDs in state.ids.
The unsorted adapter works correctly.

This leads to inconsistent behavior between adapters and potentially unstable selector outputs.

import { createEntityAdapter } from '@reduxjs/toolkit'

interface BookModel {
  id: string
  title: string
  author?: string
}

const adapter = createEntityAdapter<BookModel>({
  selectId: (book) => book.id,
  sortComparer: (a, b) => a.title.localeCompare(b.title),
})

const unsortedAdapter = createEntityAdapter<BookModel>({
  selectId: (book) => book.id,
})

const state = adapter.getInitialState()

const AClockworkOrange = { id: 'aco', title: 'A Clockwork Orange' }

const withSorted = adapter.setMany(state, [
  { ...AClockworkOrange, author: 'A' },
  { ...AClockworkOrange, title: 'Zack' },
])

const withUnsorted = unsortedAdapter.setMany(state, [
  { ...AClockworkOrange, author: 'A' },
  { ...AClockworkOrange, title: 'Zack' },
])

console.log(withSorted)   // => {ids: ['aco', 'aco'], entities: {aco: {id: 'aco', title: 'Zack'}}}
console.log(withUnsorted) // => {ids: ['aco'], entities: {aco: {id: 'aco', title: 'Zack'}}}

Expected behavior:

• Both adapters should behave consistently.
• For setMany, the last occurrence of an entity ID should be preserved.
• The state.ids array should not contain duplicates.