Convert RpcBlock to an enum that indicates availability #24986

Job	Run time
Check for 'skip-ci' label	4s
check-msrv	5m 1s
lockbud	41s
target-branch-check	3s
check-code	12m 45s
op-pool-tests	11m 43s
slasher-tests	3m 5s
http-api-tests	17m 27s
release-tests-ubuntu	16m 17s
beacon-chain-tests	14m 23s
network-tests	16m 23s
cli-check	13m 13s
ef-tests-ubuntu	8m 21s
cargo-udeps	7m 34s
cargo-sort	17s
state-transition-vectors-ubuntu	6m 54s
execution-engine-integration-ubuntu	7m 59s
basic-simulator-ubuntu	18m 9s
debug-tests-ubuntu	5m 30s
fallback-simulator-ubuntu	18m 19s
compile-with-beta-compiler	13m 34s
test-suite-success	1s
	3h 17m 43s

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