Parallelize independent verifier pairing-input computations #1001

Summary

The verifier computes two independent G1 pairing inputs sequentially:

• -(W_z + u * W_zw)
• the grouped verifier MSM

Investigate computing them concurrently with rayon::join when std is enabled. The existing behavior should remain for no_std.

Optionally a focused verification benchmark and ensure the existing verifier and soundness tests continue to pass.