Remove dependency injection from core module and data module from presentation-widget module

Includes side effects:
- No longer need to restart app for user agent string change to take effect
- parseAs extension function requires a Json instance in the calling context, which doesn't necessarily need to be the default one provided by Injekt

source-api/build.gradle.kts

@@ -10,20 +10,14 @@ android {
     defaultConfig {
         consumerProguardFile("consumer-proguard.pro")
     }
-
 }
 
 dependencies {
-
     implementation(project(":core"))
 
     api(kotlinx.serialization.json)
-
+    api(libs.injekt.core)
     api(libs.rxjava)
-
     api(libs.preferencektx)
-
     api(libs.jsoup)
-
-    implementation(androidx.corektx)
 }

source-api/src/main/java/eu/kanade/tachiyomi/source/online/HttpSource.kt

@@ -68,7 +68,7 @@ abstract class HttpSource : CatalogueSource {
      * Headers builder for requests. Implementations can override this method for custom headers.
      */
     protected open fun headersBuilder() = Headers.Builder().apply {
-        add("User-Agent", network.defaultUserAgent)
+        add("User-Agent", network.defaultUserAgentProvider())
     }
 
     /**