Use correct constraint field for curve tests and add tests for multiplication by `NonNativeFieldVar` #2583

Job	Run time
Check Style	7s
Check (stable)	12s
Check (nightly)	1m 14s
Check no_std	28s
List directories for parallelizing tests	3s
Check Documentation	55s
Test (stable)	5m 31s
Test assembly	5m 26s
Test (nightly)	10m 47s
Test (cp6_782/)	12s
Test (mnt4_753/)	1m 26s
Test (mnt6_753/)	13s
Test (./bw6_761)	55s
Test (./ed_on_mnt4_298)	1s
Test (./ed_on_mnt4_753)	1s
Test (./pallas)	1s
Test (./bn254)	51s
Test (./ed_on_cp6_782)	29s
Test (./ed25519)	1s
Test (./secq256k1)	1s
Test (./ed_on_bls12_381)	39s
Test (./secp256k1)	1s
Test (./grumpkin)	1s
Test (./bls12_377)	53s
Test (./ed_on_bw6_761)	30s
Test (./curve25519)	39s
Test (./mnt4_298)	1s
Test (./bls12_381)	56s
Test (./secp384r1)	1s
Test (./mnt6_298)	1s
Test (./bw6_767)	54s
Test (./secp256r1)	1s
Test (./ed_on_bls12_377)	40s
Test (./ed_on_bls12_381_bandersnatch)	41s
Test (./ed_on_bn254)	37s
Test (./vesta)	1s
	35m 30s

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