✨ Comprehensive bounds checking for event values

[demberto]

Problem

Till 2.2.0, non-DATA events had a value setter. In 2.2.0, I removed event value lazy evaluation entirely.

Now value is an attribute of EventBase. Structs as part of list events or child level structs didn't invoke any setters, as they were just dictionaries.

The earlier property setter failed with a ConstructError or struct.Error which was non descriptive of what really caused it.

Ideas

Make EventBase.value a descriptor again. Instead of doing everything in EventBase ctor, shift the parsing logic to subclasses.

Make this descriptor take in a validator class. For struct-based events, wrap the parsed Container into a special dictionary descriptor which validates every __setitem__ with the correct construct.

List event values could have their own list descriptor wrapper over the struct dictionary descriptors.