Fix for cloned stream that is subsequently flattened

Description

Fixes #707 (closed). The issue is if a cloned stream is subsequently flattened, the original stream is used later instead of the clone. I think this is because the InplaceVariable is not correctly updated.

Somewhat related, there is also a bug in concatenate1d when you consider the case that a stream is not truly from a 1D array, but from a flattened 2D array. I tried to use @rfforelli's fix for this, but it seems to not be quite working. Maybe he has some input?

Type of change

• Bug fix (non-breaking change that fixes an issue)

Tests

• Added a test that should fail on main but succeed on this branch

Test Configuration:

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added. (to be done later)
• I have added tests that prove my fix is effective or that my feature works.