Added some tests to address special issues and included the issues causes

[JochenHoertreiter]

there are problems with

• state_requests and guards being active even after a component got destroyed
• state_requests blocked by a guard still execute after a state is requested in sync
• multiple callbacks once a state is reached (upward or downward) were not supported. Added await for this that allows multiple subscribers. state() already uses await - if a callback is provided. Additionally enabled await/unawait for the component api.
• the vue plugin is causing performance issues if it creates CJS observers for each model field it finds. it now only creates observers if vue is calling for bindings. Had to change some orders inside the plugin for this.

Sorry for not updating the documentation about await/unawait ;)

[rse]

Thanks for your contribution, Jochen!