Share with workers a private copy of data structures set by main thread, stored on the `namespace` (`ns`) object

**Describe the feature you'd like**
The `namespace` or `ns` object is used to communicate or share data structures between the main thread and the workers and between the workers.
These data structures need to be created by the `sharer` in order to be, well, really shared and if they are mutable, they must also be protected with a kind of a lock (`RLock`), also created by `sharer`.

This allows a communication *back and forward* between the main thread and the workers and between the workers.

But in some cases it is needed something simpler: a main thread share information with its worker in one way fashion and the workers don't need to communicate between themselves. This scenario makes a fully N-to-N shared data structure and the requirement of a lock totally unnecessary.

In this case `byexample` could allow to create non-shared data-structures like plain `list`, `dict` or `int` in the main thread and make them visible in the workers as *private copies*.

To ensure that this will work in `threading` and in `multiprocessing` environments, the *private* objects must be pickle-able and the copy process should be `(take main's object)->pickle->(get the bytes)->unpickle->(get the copy object)`

**Additional context (optional)**
The documentation of `byexample` does not explain what happen if `ns` is used to store objects *not* created by `sharer`. In principle we could forbid them or we could make it private. In any case it may break some 3rd party plugin but the impact should be quite low.