chore: add Block::uncle #4753

Job	Run time
doctest	2m 41s
feature-checks	8m 10s
wasm-unknown	2m 31s
test ubuntu-latest stable --no-default-features	2m 23s
test ubuntu-latest stable	2m 39s
wasm-wasi	3m 18s
test ubuntu-latest stable --all-features	3m 11s
cfg-check	32s
test ubuntu-latest nightly --no-default-features	1m 46s
test ubuntu-latest nightly	1m 45s
check no_std	1m 3s
test ubuntu-latest nightly --all-features	2m 25s
clippy	1m 40s
test ubuntu-latest 1.79 --no-default-features	1m 35s
docs	1m 5s
test ubuntu-latest 1.79	1m 40s
test windows-latest stable --no-default-features	5m 57s
fmt	14s
test windows-latest stable	5m 58s
test windows-latest stable --all-features	6m 47s
test windows-latest nightly --no-default-features	4m 57s
test windows-latest nightly	4m 1s
test windows-latest nightly --all-features	4m 24s
test windows-latest 1.79 --no-default-features	2m 57s
test windows-latest 1.79	3m 20s
	1h 16m 59s

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