Add issue 544 proof fixtures

[1sgtpepper]

Test-only CI experiment for issue project-llzk#544. It checks two current behaviors:

• the verifier accepts unbound, multiply constrained, conditionally constrained, and use-before-constraint llzk.aux shapes;
• poly lowering can mutate IR before reporting a later unsupported operation.

This draft is evidence collection only and is not proposed for upstream merge.