feat: download blobs in `PendingBlocks` #2867

Job	Run time
Build native libraries	19s
Download Beacon Node OAPI	5s
Download spectests	6s
Lint	1m 49s
Start and stop the node	4m 1s
Test	3m 45s
Run spec-tests (capella, minimal)	3m 58s
Build project	3m 59s
Run spec-tests (capella, general)	4m 1s
Run spec-tests (capella, mainnet)	4m 0s
Run spec-tests (deneb, minimal)	3m 59s
Run spec-tests (deneb, general)	3m 59s
Run spec-tests (deneb, mainnet)	3m 58s
All spec-tests passed	1s
	38m 0s

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