🐛 [Android] namespace is not set in Karte core

[mizutani-wataru]

Expected Behavior

App can be built with gradle8.

Current Behavior

While trying to build our app with gradle8, we were getting error logs like this:

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':karte_core'.
> Could not create an instance of type com.android.build.api.variant.impl.LibraryVariantBuilderImpl.
   > Namespace not specified. Specify a namespace in the module's build file. See https://d.android.com/r/tools/upgrade-assistant/set-namespace for information about setting the namespace.

     If you've specified the package attribute in the source AndroidManifest.xml, you can use the AGP Upgrade Assistant to migrate to the namespace value in the build file. Refer to https://d.android.com/r/tools/upgrade-assistant/agp-upgrade-assistant for general information about using the AGP Upgrade Assistant.

Possible Solution

Merging of the following PR

• gradle8に対応するために、namespaceを追加 #44

Steps to Reproduce

1. flutter pub add karte_core@^1.3.0
2. flutter run

Context (Environment)

run flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.27.1, on macOS 15.2 24C101 darwin-arm64, locale ja-JP)
[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
    ! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 16.2)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2024.1)
[✓] VS Code (version 1.95.0)
[✓] Connected device (3 available)
[✓] Network resources