Add tests

[MuntashirAkon]

Test the library using unit tests. This will help the maintainers as well as developers:

1. Prevent issues due to regression by ensuring continuous testing via GitHub actions, for example
2. Developers can quickly understand how to use the library by looking at the tests.

[REAndroid]

Thank you ! This will be the next milestone. For now if you need example for implementation of this project check APKEditor

[MuntashirAkon]

Thanks for finally adding some tests. Tests should use real-life manifest files. I would suggest using AndroidManifest files from HMS Core and NP Manager. The former has the largest manifest you'll ever find, and the latter is the only known example of an AXML with a null header.