added new tests for the powertube it now succeds all tests since the uut was...

Added new powertube functionality so that the max power level is configureable.

Added by adding max power level in constructor of powertube. Also added in the cooker constructor where a _maxlevel private variable, that is obtained from the powertube, is saved. The max power level is achieved from a public function that returns the variable. The UI then can access the set max power level from the cooker to constrain the able powers you can set.

The validation of the max power level happens in the constructor of the power tube, the wattage must be between 500W and 1000W.

There has been added unit tests as well, most testing happens in the interface unit test to test that the wattage is constrained when you press the power button.

Furthermore tests has been added to the powertube (to check that exceptions are thrown when power is not within 500W-1000W). Tests for the cooker is also introduced to check you can get the desired power level (and also to get 100% code coverage)

Apart from the added new power tube features, i have merged main in to the feature branch.