chore: mark `Signature` as deprecated (#819) #2197

Job	Run time
clippy	1m 13s
check no_std	39s
docs	57s
features stable	2m 8s
features stable --all-targets	3m 16s
fmt	12s
features nightly	2m 26s
miri --no-default-features	5m 21s
features nightly --all-targets	4m 12s
miri	5m 24s
wasm	33s
miri --all-features	7m 41s
test ubuntu-latest stable --no-default-features	1m 29s
test ubuntu-latest stable	1m 9s
test ubuntu-latest nightly --no-default-features	1m 15s
test ubuntu-latest nightly	1m 21s
test ubuntu-latest 1.81 --no-default-features	36s
test ubuntu-latest 1.81	38s
test windows-latest stable --no-default-features	3m 25s
test windows-latest stable	3m 2s
test windows-latest nightly --no-default-features	2m 41s
test windows-latest nightly	3m 2s
test windows-latest 1.81 --no-default-features	1m 37s
test windows-latest 1.81	1m 37s
test ubuntu-latest 1.81 --features json	40s
test windows-latest 1.81 --features json	1m 44s
test ubuntu-latest nightly --all-features	1m 25s
test windows-latest nightly --all-features	2m 58s
ci success	2s
	1h 2m 43s

Provide feedback