refactor: replace lodash with es-toolkit

Replace lodash utility functions with es-toolkit equivalents to reduce
bundle size and improve performance. Update imports in config service
and merge-configs utility.

Author: hwibaski

lib/config.service.ts

@@ -2,9 +2,7 @@ import { Inject, Injectable, Optional } from '@nestjs/common';
 import { isUndefined } from '@nestjs/common/utils/shared.utils';
 import * as dotenv from 'dotenv';
 import fs from 'fs';
-import get from 'lodash/get';
-import has from 'lodash/has';
-import set from 'lodash/set';
+import { get, has, set } from 'es-toolkit/compat';
 import { Subject } from 'rxjs';
 import {
   CONFIGURATION_TOKEN,

lib/utils/merge-configs.util.ts

@@ -1,4 +1,4 @@
-import set from 'lodash/set';
+import { set } from 'es-toolkit/compat';
 
 /**
  * @publicApi

package-lock.json

@@ -20,7 +20,7 @@
   "dependencies": {
     "dotenv": "16.4.7",
     "dotenv-expand": "12.0.2",
-    "lodash": "4.17.21"
+    "es-toolkit": "^1.39.3"
   },
   "devDependencies": {
     "@commitlint/cli": "19.8.1",