Storage bug fixes - Githubissues

Description

Bug fixes in citylearn.energy_model.Storage and how electricity consumption when charging storage devices is calculated.

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Fixed possibility of citylearn.energy_model.Storage.energy_init less than 0 which, is not physically possible.
Fixed case where charged energy is less than what is prescribed by controller causing electricity consumption by storage device to be overestimated.

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[x] I have tested the changes locally and they work as intended.
[x] I have updated the documentation, if applicable.
[x] I have added new tests, if applicable.
[x] I have added any required dependencies to the requirements.txt file, if applicable.
[x] I have followed the project's code style and conventions.

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