feat: Add dependency injection and application class

This commit introduces Koin for dependency injection and sets up an application class.

Changes:

- Added `TechExactlyApplication` class to initialize Koin.
- Declared the `TechExactlyApplication` in the `AndroidManifest.xml`.
- Created `AppModule` to define dependencies, including Retrofit, the User API, and the User repository.
- Added the Koin dependency.
- `AppModule` created with the following:
  - `provideRetrofit`: for providing Retrofit instance
  - `provideUserApi`: for providing UserApi instance
  - `UserRepository`: for providing repository instance

Author: CGreenP

app/src/main/AndroidManifest.xml

@@ -5,6 +5,7 @@
     <uses-permission android:name="android.permission.INTERNET" />
 
     <application
+        android:name=".TechExactlyApplication"
         android:allowBackup="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
         android:fullBackupContent="@xml/backup_rules"

app/src/main/java/com/example/techexactly/TechExactlyApplication.kt

@@ -0,0 +1,16 @@
+package com.example.techexactly
+
+import android.app.Application
+import com.example.techexactly.di.appModule
+import org.koin.android.ext.koin.androidContext
+import org.koin.core.context.startKoin
+
+class TechExactlyApplication : Application() {
+    override fun onCreate() {
+        super.onCreate()
+        startKoin {
+            androidContext(this@TechExactlyApplication)
+            modules(appModule)
+        }
+    }
+}

app/src/main/java/com/example/techexactly/di/AppModule.kt

@@ -0,0 +1,12 @@
+package com.example.techexactly.di
+
+import com.example.techexactly.model.network.provideRetrofit
+import com.example.techexactly.model.network.provideUserApi
+import com.example.techexactly.model.repository.UserRepository
+import org.koin.dsl.module
+
+val appModule = module {
+    single { provideRetrofit() }
+    single { provideUserApi(get()) }
+    single { UserRepository(get()) }
+}