feat(core): export trackBy and trackByDeep separately

npm/ng-packs/packages/core/src/lib/services/track-by.service.ts

@@ -1,15 +1,17 @@
 import { Injectable, TrackByFunction } from '@angular/core';
 import { O } from 'ts-toolbelt';
 
+export const trackBy = <T = any>(key: keyof T): TrackByFunction<T> => (_, item) => item[key];
+
+export const trackByDeep = <T = any>(
+  ...keys: T extends object ? O.Paths<T> : never
+): TrackByFunction<T> => (_, item) => keys.reduce((acc, key) => acc[key], item);
+
 @Injectable({
   providedIn: 'root',
 })
 export class TrackByService<ItemType = any> {
-  by<T = ItemType>(key: keyof T): TrackByFunction<T> {
-    return (_, item) => item[key];
-  }
+  by = trackBy;
 
-  byDeep<T = ItemType>(...keys: T extends object ? O.Paths<T> : never): TrackByFunction<T> {
-    return (_, item) => keys.reduce((acc, key) => acc[key], item);
-  }
+  byDeep = trackByDeep;
 }