refactor(api/rest): create internal constructor for tests

api/rest/src/commonMain/kotlin/moe/lava/neon/api/ApiClient.kt

@@ -20,7 +20,12 @@ import kotlinx.serialization.ExperimentalSerializationApi
 import moe.lava.neon.common.captcha.CaptchaRequest
 import moe.lava.neon.common.captcha.CaptchaResponse
 
-class ApiClient {
+class ApiClient internal constructor(
+    engine: HttpClientEngine,
+    assertSuccess: Boolean,
+) {
+    constructor() : this(HttpClient().engine, true)
+
     private val logger = Logger.withTag("neon.core.api/client")
 
     private var captchaHandler: (suspend (CaptchaRequest) -> CaptchaResponse)? = null
@@ -30,8 +35,8 @@ class ApiClient {
     }
 
     @OptIn(ExperimentalSerializationApi::class)
-    internal val client = HttpClient {
-        expectSuccess = true
+    internal val client = HttpClient(engine) {
+        expectSuccess = assertSuccess
         install(ContentNegotiation) {
             json(ApiConstants.json)
         }

core/src/commonMain/kotlin/moe/lava/neon/core/di/CoreModule.kt

@@ -11,7 +11,7 @@ import org.koin.dsl.module
 import org.koin.plugin.module.dsl.single
 
 val coreModule = module {
-    single<ApiClient>()
+    factory { ApiClient() }
     single<AppSettings>()
 
     single<AuthRepository>()