add a test for connect_four

[alessandrofelder]

Description

What is this PR

• Bug fix (partial)
• Addition of a new feature
• Other

Why is this PR needed?

We would like to prevent #383 to happen again.

What does this PR do?
Writes a test for connect_four that reproduces #383, so we know it's fixed once we fix it.
For now, the test is marked as XFAIL (expected to fail) - this test is the minimal example needed to justify why we need to use uint32 for the signal_array (for cases where we have >65535 - possibly temporary - struct_ids - see #386 )

I am reluctant to add assertions in the highly optimised part of the code, as this may affect performance.

References

A step on the way to closing #383.

How has this PR been tested?

The PR adds a well-documented test that was run locally.

Is this a breaking change?

No.

Does this PR require an update to the documentation?

No.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality (unit & integration)
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[willGraham01]

👍