Upgrade ImmutableStrategy

[pedrorrivero]

What is the expected enhancement?

Currently, ImmutableStrategy updates __new__() and configures __repr__() to dynamically include the args passed to __init__().

There are cases, nonetheless, where we do not want some of those args to be included in repr, so exceptions have to be hardcoded into the class, forcing updates to ImmutableStrategy to create a child class. Ideally we would like to avoid this, letting the user specify which args to include and which not to.

Also, there are better ways to enforce immutability based on meta-programming concepts (e.g. __slots__, descriptors).