Add hashing to `secp256k1` #2961

Job	Run time
Check Style	13s
Test (stable)	9m 12s
Check (stable)	2m 27s
Test (nightly)	17m 31s
Check (nightly)	1m 11s
List directories for parallelizing tests	5s
Check Documentation	1m 2s
Check no_std	28s
Test assembly	8m 25s
Test (cp6_782/)	28m 46s
Test (mnt4_753/)	13m 14s
Test (mnt6_753/)	29m 1s
Test (./ed_on_mnt4_753)	3m 57s
Test (./secp256r1)	1m 0s
Test (./ed_on_mnt4_298)	1m 15s
Test (./ed_on_cp6_782)	1m 25s
Test (./mnt4_298)	3m 55s
Test (./mnt6_298)	5m 28s
Test (./ed_on_bn254)	1m 12s
Test (./bn254)	2m 15s
Test (./secp256k1)	1m 3s
Test (./bw6_761)	3m 55s
Test (./bls12_377)	4m 3s
Test (./grumpkin)	1m 25s
Test (./secp384r1)	1m 37s
Test (./ed_on_bls12_377)	1m 5s
Test (./secq256k1)	54s
Test (./ed25519)	1m 5s
Test (./ed_on_bls12_381)	1m 20s
Test (./ed_on_bw6_761)	36s
Test (./curve25519)	1m 18s
Test (./ed_on_bls12_381_bandersnatch)	1m 11s
Test (./pallas)	1m 14s
Test (./vesta)	1m 7s
Test (./bw6_767)	4m 0s
Test (./bls12_381)	3m 18s
	2h 41m 13s

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