Allow selecting a precision / decimal places per sub-component

https://forums.adafruit.com/viewtopic.php?t=222716

Basically users want to format their data to a specific decimal places.

When converting Celsius @ 3dp to Fahrenheit, it ends up with a large number of decimal places after rounding and that gets published.

Start with the linked Adafruit forum discussion to clarify the requested formatting behavior. Then trace how sub-components convert and publish values in the C++/Arduino project. Done means each sub-component can select its decimal precision and converted Celsius/Fahrenheit data is published with that precision.

Written by the indexing model from the issue text.