feat(ring_theory/tensor_product): add assoc for tensor product as an algebra homomorphism (#13309)
feat(ring_theory/tensor_product): add assoc for tensor product as an algebra homomorphism (#13309)

By speeding up a commented out def, this goes from from ~100s to ~7s on my machine .


Co-authored-by: Scott Morrison <625600233cb3bcab32268c17610882e0fdaed295@tqft.net>





leanprover-community/mathlib,leanprover-community/mathlib