feat: add Signature trait #2153

Job	Run time
clippy	1m 8s
check no_std	1m 2s
docs	55s
features stable	2m 6s
fmt	12s
features stable --all-targets	3m 31s
miri --no-default-features	4m 57s
features nightly	2m 25s
miri	5m 7s
features nightly --all-targets	3m 24s
test ubuntu-latest stable --no-default-features	1m 9s
wasm	35s
miri --all-features	7m 38s
test ubuntu-latest stable	1m 22s
test ubuntu-latest nightly --no-default-features	1m 21s
test ubuntu-latest nightly	1m 16s
test ubuntu-latest 1.79 --no-default-features	37s
test ubuntu-latest 1.79	40s
test windows-latest stable --no-default-features	3m 36s
test windows-latest stable	3m 32s
test windows-latest nightly --no-default-features	2m 54s
test windows-latest nightly	2m 50s
test windows-latest 1.79 --no-default-features	1m 15s
test windows-latest 1.79	1m 35s
test ubuntu-latest 1.79 --features json	38s
test windows-latest 1.79 --features json	1m 30s
test ubuntu-latest nightly --all-features	1m 26s
test windows-latest nightly --all-features	2m 57s
ci success	2s
	1h 1m 40s

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