refactor: enable strict analysis options and fix type safety across codebase

Enable strict-casts, strict-inference, and strict-raw-types in
analysis_options.yaml. Add custom_lint with riverpod_lint. Fix all
resulting type warnings with explicit type parameters and safer casts.

Also improves APK update checker to detect device ABIs for correct
variant selection and fixes Deezer artist name parsing edge case.

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -304,6 +304,7 @@ class MainActivity: FlutterFragmentActivity() {
             ".mp3" -> "audio/mpeg"
             ".opus" -> "audio/ogg"
             ".flac" -> "audio/flac"
+            ".lrc" -> "application/octet-stream"
             else -> "application/octet-stream"
         }
     }