fix: lock release when there is a python error

[inimaz]

Before

If there was an error in the user's code

tracker.start()

raise ValueError()

tracker.stop() <== this line is never called

the lock will not be removed. Meaning the next time you run the same script, you will get an error Error: Another instance of codecarbon is already running. Turn off the other instance to be able to run this one. Exiting.

Now

The lock is removed even if:

• the user does Ctl + C to terminate the script
• there is a python error in between start and stop
• Some other error terminates it

[benoit-cty]

Congratulation for finding a solution !
atexit and signal are included Python library so no need to create new dependencies, nice.