Add example app and use it to improve test suite

[UberMouse]

The test-app used by the current tests is... lacking. It was a simple attempt at todo-mvc from way back when this library was first created back in 2020 and has grown and changed randomly as the test suite needed it over the years. It does not provide enough testing flexibility either so it doesn't even fulfill it's only purpose very well

Need to create a new xstate-tree example app, with a good test suite, both to provide a good piece of documentation on what an xstate-tree app looks like and how to test one, as well as increase the testing confidence.