fix: make `Block::hash` required #3625

Job	Run time
wasm-unknown	51s
no-std	20s
doctest	1m 5s
test ubuntu-latest stable --no-default-features	1m 22s
wasm-wasi	1m 9s
test ubuntu-latest stable	1m 15s
clippy	41s
test ubuntu-latest stable --all-features	1m 58s
docs	53s
feature-checks	3m 3s
test ubuntu-latest nightly --no-default-features	1m 17s
test ubuntu-latest nightly	1m 4s
cfg-check	28s
test ubuntu-latest nightly --all-features	2m 2s
fmt	12s
test ubuntu-latest 1.76 --no-default-features	38s
test ubuntu-latest 1.76	36s
test windows-latest stable --no-default-features	4m 11s
test windows-latest stable	3m 46s
test windows-latest stable --all-features	5m 8s
test windows-latest nightly --no-default-features	3m 33s
test windows-latest nightly	3m 41s
test windows-latest nightly --all-features	4m 35s
test windows-latest 1.76 --no-default-features	2m 13s
test windows-latest 1.76	3m 17s
	49m 18s

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