CI: strengthen downstream tensor checks

[Krastanov-agent]

Summary

• add Gabs and SecondQuantizedAlgebra to active reverse-dependency testing
• test downstream packages from a temporary outer environment that develops both checkouts
• add a filtered ecosystem smoke test for shared tensor bindings, unsupported zero arity, and tensor ambiguities

This is a CI-only follow-up to the QuantumInterface 0.4.4 downstream migration and should land after the downstream releases.

Validation

• Julia syntax parsing for both workflow helper scripts
• git diff --check

Changelog

Skip-Changelog

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 34.22%. Comparing base (4d9df4e) to head (c1cee8e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
+ Coverage   34.00%   34.22%   +0.22%     
==========================================
  Files          15       15              
  Lines         450      450              
==========================================
+ Hits          153      154       +1     
+ Misses        297      296       -1     

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[Krastanov-agent]

Maintainer note: this is a CI-only PR and should carry the Skip-Changelog label. The contributor token cannot add labels. The current changelog check failure is therefore expected until a maintainer applies it.