feat(consensus): `signer` field in `Signed` tx. #1723

Job	Run time
cfg-check	1m 32s
clippy	37s
docs	1m 58s
doctest	1m 17s
feature-checks	38s
fmt	14s
no-std	22s
wasm-unknown	49s
test stable --no-default-features	1m 27s
wasm-wasi	1m 20s
test stable	1m 52s
test stable --all-features	2m 9s
test nightly --no-default-features	2m 47s
test nightly	2m 38s
test nightly --all-features	3m 2s
test 1.76 --no-default-features	45s
test 1.76	49s
	24m 16s

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