Update / fix MeterValues format

[matth-x]

Change the data type of the default EnergyMeterInput to int.

It may be necessary to patch the data format in the host system integration. For example, the previous usage

setEnergyMeterInput([] () -> float {
    return /* energy_register */;
});

would become

setEnergyMeterInput([] () -> int {
    return /* (int) energy_register */;
});

Furthermore, this PR fixes the float format in MeterValues which contained white spaces in some scenarios (e.g. " 0.0"). If the float format doesn't suit the application, the firmware can override it by setting the build flag MO_SAMPLEDVALUE_FLOAT_FORMAT (default: "%.2f")