Check slashability of attestations in batches to avoid sequential bottleneck #17961

Job	Run time
dockerfile-ubuntu	1m 0s
doppelganger-protection-failure-test	1s
doppelganger-protection-success-test	1s
run-local-testnet	1s
checkpoint-sync-test-${{ matrix.network }}	1s
genesis-sync-test-${{ matrix.fork }}-${{ matrix.offline_secs }}s	1s
local-testnet-success	1s
	1m 6s

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