consensus: impl `recover_signers` for `BlockBody<TxEnvelope>` #4686

Job	Run time
wasm-unknown	2m 47s
docs	1m 43s
clippy	1m 17s
doctest	3m 30s
check no_std	1m 9s
feature-checks	5m 6s
wasm-wasi	3m 34s
test ubuntu-latest stable --no-default-features	2m 54s
cfg-check	1m 5s
test ubuntu-latest stable	2m 49s
fmt	11s
test ubuntu-latest stable --all-features	3m 20s
test ubuntu-latest nightly --no-default-features	2m 20s
test ubuntu-latest nightly	2m 29s
test ubuntu-latest nightly --all-features	2m 54s
test ubuntu-latest 1.79 --no-default-features	2m 3s
test ubuntu-latest 1.79	1m 47s
test windows-latest stable --no-default-features	6m 10s
test windows-latest stable	5m 48s
test windows-latest stable --all-features	6m 19s
test windows-latest nightly --no-default-features	5m 11s
test windows-latest nightly	6m 17s
test windows-latest nightly --all-features	6m 13s
test windows-latest 1.79 --no-default-features	5m 46s
test windows-latest 1.79	4m 41s
	1h 27m 23s

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