Fix: use unique value for NOT_FOUND

[romgrk]

I'm not sure what's the reasoning for using a string constant for the not-found value, but an object feels both safer (real uniqueness, the string 'NOT_FOUND' could make the logic fail) and more performant (no strcmp() if both values are strings) which is handy when the selectors are called very often.

I've used a private class instance for the empty value because you seem to use the value type NOT_FOUND_TYPE, otherwise I would have gone with a Symbol('not-found') or an empty object, but any of these would be fine I think.

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[aryaemami59]

Seems like a good idea. Though I think in this particular scenario a export const NOT_FOUND = Symbol('NOT_FOUND') will be fine. And now if you add a test to lruMemoize.test.ts:

test('cache miss identifier does not collide with state values', () => {
    const state = ['NOT_FOUND', 'FOUND']

    type State = typeof state

    const createSelector = createSelectorCreator({
      memoize: lruMemoize,
      argsMemoize: lruMemoize
    }).withTypes<State>()

    const selector = createSelector(
      [(state, id: number) => state[id]],
      state => state,
      {
        argsMemoizeOptions: { maxSize: 10 },
        memoizeOptions: { maxSize: 10 }
      }
    )

    const firstResult = selector(state, 0)

    expect(selector(state, 1)).toBe(selector(state, 1))

    const secondResult = selector(state, 0)

    expect(secondResult).toBe('NOT_FOUND')

    expect(firstResult).toBe(secondResult)

    expect(selector.recomputations()).toBe(2)
  })

It would have failed previously as NOT_FOUND would cause a cache miss and selector.recomputations() would be 3 instead of 2. But now it should be good.

[romgrk]

I have added the suggested modifications.