add formatting options for exponentformat: "power" to provide normalised scientific notation

Hi,

Setting exponentformat to "power" can sometimes display numbers in a format: 0.a × 10^b . We teach the normalised scientific notation (https://en.wikipedia.org/wiki/Scientific_notation#Normalized_notation), in which the number before the decimal place must be greater than or equal to 1, and less than 10.

I couldn't see a way of setting Plotly to use this notation ("tickformat" options don't seem to expose this either), and was wondering whether it could be implemented?

Thanks for your time (and for Plotly, which is great!)

Comienza rastreando cómo Plotly gestiona la opción exponentformat y cómo se aplica tickformat. Compara la salida existente "power" con la notación científica normalizada, en la que la mantisa es como mínimo 1 y menor que 10. Se considera terminado cuando una opción de formato documentada produce esa notación de forma coherente, con pruebas que cubran valores representativos.