vtkPythonStdStreamCaptureHelper: support doctests
Our stream wrapper is missing some APIs to faithfully impersonate a stream: https://docs.python.org/3/library/io.html#id1
Cc: @dgobbi
Our stream wrapper is missing some APIs to faithfully impersonate a stream: https://docs.python.org/3/library/io.html#id1
Cc: @dgobbi