Add inFlight method for effects

[sergeysova]

import { createEffect } from 'effector';
import { inFlight } from 'patronum/in-flight';

const loadFirst = createEffect().use(() => Promise.resolve(null));
const loadSecond = createEffect().use(() => Promise.resolve(2));
const $count = inFlight({ effects: [loadFirst, loadSecond] });

$count.watch((count) => console.info(`count: ${count}`));
// => count: 0

loadFirst();
loadSecond();
// => count: 2

loadSecond();
loadSecond();
// => count: 4

// Wait to resolve all effects
// => count: 0

---

With domain support:

import { createDomain } from 'effector';
import { inFlight } from 'patronum/in-flight';

const app = createDomain();
const loadFirst = app.createEffect().use(() => Promise.resolve(null));
const loadSecond = app.createEffect().use(() => Promise.resolve(2));
const $count = inFlight({ domain: app });

$count.watch((count) => console.info(`count: ${count}`));
// => count: 0

loadFirst();
loadSecond();
// => count: 2

loadSecond();
loadSecond();
// => count: 4

// Wait to resolve all effects
// => count: 0