chore: improve codebase with some clippy suggestions #3068

Job	Run time
Check (stable)	12s
Check no_std	29s
Check (nightly)	1m 4s
List directories for parallelizing tests	5s
Check Documentation	54s
Check Style	7s
Test (stable)	8m 56s
Test (nightly)	17m 42s
Test assembly	8m 33s
Test (cp6_782/)	5s
Test (mnt4_753/)	21m 55s
Test (mnt6_753/)	12s
Test (./ed_on_mnt4_753)	3m 50s
Test (./secp256r1)	1m 5s
Test (./ed_on_mnt4_298)	1m 8s
Test (./ed_on_cp6_782)	1m 21s
Test (./mnt4_298)	3m 50s
Test (./mnt6_298)	5m 22s
Test (./ed_on_bn254)	58s
Test (./bn254)	2m 15s
Test (./secp256k1)	1m 6s
Test (./bw6_761)	3m 47s
Test (./bls12_377)	4m 9s
Test (./grumpkin)	1m 7s
Test (./secp384r1)	1m 16s
Test (./ed_on_bls12_377)	1m 3s
Test (./secq256k1)	1m 0s
Test (./ed25519)	54s
Test (./ed_on_bls12_381)	1m 9s
Test (./ed_on_bw6_761)	35s
Test (./curve25519)	1m 1s
Test (./ed_on_bls12_381_bandersnatch)	1m 2s
Test (./pallas)	1m 10s
Test (./vesta)	1m 3s
Test (./bw6_767)	3m 59s
Test (./bls12_381)	3m 14s
	1h 47m 38s

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