* refactor: `Slot.source` replaced with `Slot.fill_node`, new `Component.node` property, and `slot_node` available in `on_slot_rendered()` hook.
* refactor: fix windows path error in tests
* feat: add decorator for writing component tests
* refactor: udpate changelog + update deps pins
* refactor: fix deps
* refactor: make cached_ref into generic and fix linter errors
* refactor: fix coverage testing
* refactor: use global var instead of env var for is_testing state