Add test for attach generic factories support

This commit should fail

src/types/__tests__/effector/attach.test.ts

@@ -1,5 +1,5 @@
 /* eslint-disable no-unused-vars */
-import {createStore, createEffect, attach, Effect} from 'effector'
+import {createStore, createEffect, attach, sample, Effect} from 'effector'
 
 const typecheck = '{global}'
 
@@ -34,6 +34,30 @@ describe('explicit generics', () => {
   })
 })
 
+test('factories with generics support', () => {
+  function createModel<T>() {
+    const $data = createStore<T | null>(null)
+
+    const loadFx = attach({
+      source: {
+        /* Assume we use some $api with external API we don't control */
+      },
+      effect() {
+        const result: any = /* API returns `any` */ null
+
+        return result as T /* explicit cast, becase we know result is T */
+      },
+    })
+
+    sample({clock: loadFx.doneData, target: $data})
+  }
+  expect(typecheck).toMatchInlineSnapshot(`
+    "
+    no errors
+    "
+  `)
+})
+
 describe('with source', () => {
   test('with single store (should pass)', () => {
     const foo = createStore<string>('foo')