Use correct constraint field for curve tests and add tests for multiplication by `NonNativeFieldVar` #2587

Job	Run time
List directories for parallelizing tests	4s
Check no_std	34s
Check (stable)	23s
Check (nightly)	1m 9s
Check Documentation	1m 0s
Test (stable)	5m 24s
Test (nightly)	10m 57s
Check Style	17s
Test assembly	5m 21s
Test (cp6_782/)	18s
Test (mnt4_753/)	20m 52s
Test (mnt6_753/)	33m 21s
Test (./bw6_761)	2m 48s
Test (./ed_on_mnt4_298)	53s
Test (./ed_on_mnt4_753)	1m 44s
Test (./pallas)	1m 13s
Test (./bn254)	1m 59s
Test (./ed_on_cp6_782)	58s
Test (./ed25519)	59s
Test (./secq256k1)	58s
Test (./ed_on_bls12_381)	1m 17s
Test (./secp256k1)	1m 8s
Test (./grumpkin)	1m 17s
Test (./bls12_377)	3m 23s
Test (./ed_on_bw6_761)	38s
Test (./curve25519)	59s
Test (./mnt4_298)	2m 7s
Test (./bls12_381)	3m 13s
Test (./secp384r1)	51s
Test (./mnt6_298)	3m 2s
Test (./bw6_767)	2m 54s
Test (./secp256r1)	57s
Test (./ed_on_bls12_377)	1m 6s
Test (./ed_on_bls12_381_bandersnatch)	56s
Test (./ed_on_bn254)	51s
Test (./vesta)	1m 7s
	1h 56m 58s

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