poc(scanner): get started with the blockchain scanner proof of concept #48

Job	Run time
Generate crates matrix	11s
Check crates matrix	10s
Build tower-batch-control crate	54s
Build tower-fallback crate	33s
Build zebra-chain crate	3m 54s
Build zebra-consensus crate	15m 40s
Build zebra-network crate	4m 16s
Build zebra-node-services crate	3m 20s
Build zebra-rpc crate	20m 57s
Build zebra-scanner crate	13m 44s
Build zebra-script crate	2m 51s
Build zebra-state crate	17m 0s
Build zebra-test crate	1m 15s
Build zebra-utils crate	15m 21s
Build zebrad crate	26m 46s
Open or update issues for building crates individually failures	0s
	2h 6m 52s

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