perf: re-inline always addmul #870

Job	Run time
Feature checks	31s
test (stable, --no-default-features)	1m 18s
Cargo deny check	28s
Clippy	46s
test (stable)	1m 19s
Coverage	2m 3s
test (stable, --all-features)	2m 21s
Docs	47s
Fmt	13s
test (beta, --no-default-features)	1m 23s
test (beta)	1m 22s
test (beta, --all-features)	2m 28s
test (nightly, --no-default-features)	1m 15s
test (nightly)	1m 14s
test (nightly, --all-features)	2m 16s
test (1.65, --no-default-features)	21s
test (1.65)	21s
Accept	1s
	20m 27s

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