Improve compatibility with current Flutter, Android, and iOS

[tulioccalazans]

This PR updates the package to improve compatibility with newer Flutter versions and the latest Android and iOS build requirements.

Changes

1. Handle the AppLifecycleState.hidden state introduced by newer Flutter versions.
2. Update the Android build configuration:
3. Add the required namespace.
4. Upgrade compileSdkVersion to 35.
5. Configure Java and Kotlin compatibility for Java 17.
6. Add support for Swift Package Manager (SPM) on iOS.
7. Recreate the example project using the current Flutter project structure.
8. Remove the legacy example_old project and its associated Android, iOS, and Flutter source files.

These changes are intended to keep the package compatible with current Flutter tooling and modern Android and iOS development environments.

Maintainer

I noticed that the project is currently looking for maintainers.

I have been using and working on this package and would be interested in helping maintain it going forward. I would be happy to contribute not only with this PR, but also with future updates, bug fixes, dependency upgrades, and compatibility with new Flutter, Android, and iOS versions.

If you are open to it, I would be glad to discuss becoming a maintainer or co-maintainer of the project.