rxpy3-examples: Fixing the multiple observer example

As I was adding a test for the examples/rx3_buffer_example.py I noticed that the endless while-loop was actually never called, because observable.connect() seems to be a blocking operation, until the stream finishes with on_error or on_complete.

To make this example testable, I changed the dequeue() from using an endless while-loop to emitting a list of items. The changes can bee seen in this commit.

In addition, I made a small change to the capture_stdout_as_list context-manager: I renamed the to_string()-method to __str__(), so that the context-manager’s result can be used in the test assertions using str(result) instead of result.to_string(). It does look a little nicer, and I guess that this could be called “more pythonic”.

See also