Storage get count

[Tigo-cmd]

Update DBStorage and FileStorage, adding two new methods. All changes should be done in the branch storage_get_count:

A method to retrieve one object:

Prototype: def get(self, cls, id):
    cls: class
    id: string representing the object ID
Returns the object based on the class and its ID, or None if not found

A method to count the number of objects in storage:

Prototype: def count(self, cls=None):
    cls: class (optional)
Returns the number of objects in storage matching the given class. If no class is passed, returns the count of all objects in storage.

Don’t forget to add new tests for these 2 methods on each storage engine.