✨ Comprehensive bounds checking for event values

### 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.