Rule: `no-implicit-undefined`

`undefined` used in Effector as a marker for skipping update in store. It can be hard to understand, if `undefined` is implicit used in store. E.g.
```ts
const $list = createStore([]);

const $item = $list.map(head);
```
This code will skip update if `$list` has an empty array.

The rule ought to forbid implicit usage of `undefined` in stores and mappers.