Enforce superclasses of base rounds to always define required attributes

[jmoreira-valory]

Is your feature request related to a problem? Please describe. Some base rounds require a number of base attributes to be defined by the superclasses. For example, none_type on CollectSameUntilThresholdRound.

If the superclass fails to initialize these attributes, the business logic will proceed without a warning. However, if during the execution variable is required to launch an event, it will crash the application when accessing that attribute.

Describe the solution you'd like In summary, the application should throw a warning or exception when these required attributes are not initialized. This applies to several other base round classes.

Describe alternatives you've considered

Additional context