refactor(models): ubah inheritance model ke base class

- Mengubah inheritance pada semua model di `Modules/Lpj` dari `Model` ke `Base` untuk konsistensi struktur.
- Menghapus model `SLA` beserta migrasi terkait karena tidak lagi digunakan.

database/migrations/2024_10_28_095337_create_s_l_as_table.php

@@ -1,27 +0,0 @@
-<?php
-
-use Illuminate\Database\Migrations\Migration;
-use Illuminate\Database\Schema\Blueprint;
-use Illuminate\Support\Facades\Schema;
-
-return new class extends Migration
-{
-    /**
-     * Run the migrations.
-     */
-    public function up(): void
-    {
-        Schema::create('sla', function (Blueprint $table) {
-            $table->id();
-            $table->timestamps();
-        });
-    }
-
-    /**
-     * Reverse the migrations.
-     */
-    public function down(): void
-    {
-        Schema::dropIfExists('sla');
-    }
-};