Zebra: Missing copy constraint in halo2_gadgets variable-base scalar multiplication allows under-constrained base, breaking Orchard Action circuit soundness

Summary A soundness vulnerability in the variable-base scalar multiplication gadget of halo2gadgets allowed a malicious prover to produce a valid proof for an Orchard Action with an under-constrained base point. Because this gadget enforces the diversified-address-integrity condition of the Orcha...