Filter hanging co-simulation

[trevorhardy]

Describe the bug
The inclusion of the filter in the "delayed-pi-exchange" (unmaintained) example causes the co-simulation to hang.

What is the expected behavior?
Co-simulation should run to completion when a filter is included.

To Reproduce
Run "delayed-pi-exchange" example in "delayed-pi-exchange" branch.

Environment (please complete the following information):

• Operating System: Mac
• Language Extension: Python 3.11.0
• what compiler or setup process did you use: pip install helics[cli]
• HELICS version: 3.4.0

$ helics_app --version: 3.4.0 (2023-01-19)

Additional context and information
Commenting out the filter in pisender.py allows the co-simulation to run to completion.

[trevorhardy]

Example has been moved to here; confirmed still hangs in with v3.6.0

[trevorhardy]

Similar behavior (hanging co-simulation) is seen with the User Guide "native filter" example.