rpc: add `uncle_block_from_header` impl and test #4760

Job	Run time
wasm-wasi	3m 21s
test ubuntu-latest stable --no-default-features	2m 15s
check no_std	58s
test ubuntu-latest stable	2m 24s
clippy	1m 30s
docs	1m 10s
test ubuntu-latest stable --all-features	2m 58s
doctest	2m 45s
test ubuntu-latest nightly --no-default-features	1m 42s
feature-checks	5m 39s
wasm-unknown	2m 15s
test ubuntu-latest nightly	1m 34s
test ubuntu-latest nightly --all-features	2m 8s
cfg-check	32s
fmt	15s
test ubuntu-latest 1.79 --no-default-features	1m 34s
test ubuntu-latest 1.79	1m 32s
test windows-latest stable --no-default-features	5m 30s
test windows-latest stable	5m 27s
test windows-latest stable --all-features	5m 30s
test windows-latest nightly --no-default-features	4m 41s
test windows-latest nightly	4m 19s
test windows-latest nightly --all-features	5m 29s
test windows-latest 1.79 --no-default-features	3m 51s
test windows-latest 1.79	3m 32s
	1h 12m 51s

Provide feedback