test: remove log truncation in subprocess tests

[kfundecmcsa]

The subprocess test runner was truncating captured output to 160 lines, hiding important failure details. Show the full output so developers can diagnose test failures without re-running locally.

[Copilot]

Pull request overview

This PR improves debuggability of requires_matterjs tests that run under the subprocess harness by removing output truncation, ensuring full child-process stdout/stderr is shown on failures.

Changes:

• Removed the 160-line truncation logic for captured subprocess output in failure assertions.
• Always includes the full captured output in the raised AssertionError to aid diagnosis.

[cleithner-comcast]

Where the change we talked about to make all the tests not output unless failed (and not some tests)?

[kfundecmcsa]

Where the change we talked about to make all the tests not output unless failed (and not some tests)?

Cause I forgot...

I looked into it, it's a bit more complicated than this fix, I'll keep at it

[tleacmcsa]

Where the change we talked about to make all the tests not output unless failed (and not some tests)?

Cause I forgot...

I looked into it, it's a bit more complicated than this fix, I'll keep at it

Should this PR go back to draft?

[kfundecmcsa]

Where the change we talked about to make all the tests not output unless failed (and not some tests)?

Cause I forgot...
I looked into it, it's a bit more complicated than this fix, I'll keep at it

Should this PR go back to draft?

yes - done