Removed `@Slot()` decorators #23

Job	Run time
build (3.8, pyqt5)	39s
build (3.8, pyqt6)	43s
build (3.9, pyqt5)	37s
build (3.9, pyqt6)	41s
build (3.10, pyqt5)	48s
build (3.10, pyqt6)	38s
build (3.11, pyqt5)	36s
build (3.11, pyqt6)	37s
Indicate completion to coveralls.io	11s
	5m 30s

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