Draft: Fixed wrong return type hint and updated doc string

[MyGodItsFull0fStars]

Hi, I made some changes to the stop_task(...) function of the BaseEmissionTracker class.

I changed the return type from float to the actual return type EmissionsData.
This was probably an oversight, as in almost every other function the return type is a float.

I also changed the return type in the doc-string from None to the actual one.

[benoit-cty]

Hello,
Thanks, I think it's a good idea. It's a breaking change so it needs to be put in a major release, and do the same things on all methods.

[MyGodItsFull0fStars]

Hello,
okay, when I have time I can add more of these changes to this branch, which can later be merged for a major release.

Thanks for letting me know :)