Reduce precision in returned fronius values to meaningful digits

[nielstron]

Proposed change

As per request of a user, the number of digits in returned floating point values is reduced with this patch.

This makes sense as per default, the Fronius module returns values that have up to 10 digits which usually is only due to conversion of certain limited-bit values to the JSON format. Examples may be found below

         "SMARTMETER_POWERAPPARENT_01_F64" : 1768.1400000000001,
         "SMARTMETER_POWERAPPARENT_MEAN_01_F64" : 1723.7711666666655,
         "SMARTMETER_POWERAPPARENT_MEAN_SUM_F64" : 1768.1400000000001,

The fronius native interface shows not more than two digits and since this amount of digits drastically reduces readability, it is automatically removed in this module.
The backend package is not changed as the very precise result might be still of importance in other use cases.

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[Drafteed]

easier, more clear and reduced get:

self._state = state.get("value")
if isinstance(self._state, float):
    self._state = round(self._state, 2)

[janiversen]

looks good.

[janiversen]

thanks.