perf: use bitwise operations in add/sub impls #925

Job	Run time
Docs	50s
Docs	52s
Clippy	50s
Clippy	49s
Feature checks	1m 1s
Feature checks	1m 40s
Cargo deny check	22s
Cargo deny check	21s
Fmt	11s
Fmt	14s
test (stable, --no-default-features)	1m 38s
test (stable, --no-default-features)	1m 2s
test (stable)	1m 32s
test (stable)	58s
test (stable, --all-features)	1m 8s
test (stable, --all-features)	2m 13s
test (beta, --no-default-features)	1m 33s
test (beta, --no-default-features)	1m 35s
test (beta)	1m 36s
test (beta)	1m 34s
test (beta, --all-features)	1m 13s
test (beta, --all-features)	2m 34s
test (nightly, --no-default-features)	1m 28s
test (nightly, --no-default-features)	1m 29s
test (nightly)	1m 25s
test (nightly)	1m 26s
test (nightly, --all-features)	1m 10s
test (nightly, --all-features)	2m 12s
test (1.65, --no-default-features)	38s
test (1.65, --no-default-features)	27s
test (1.65)	42s
test (1.65)	26s
Accept	0s
Accept	1s
	37m 10s

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