add(mining): Restore internal miner #1910

Job	Run time
Generate crates matrix	11s
Check crates matrix	3s
Build zebrad crate	6m 18s
Build zebra-utils crate	5m 17s
Build zebra-test crate	1m 31s
Build zebra-state crate	5m 19s
Build zebra-script crate	3m 29s
Build zebra-rpc crate	1s
Build zebra-node-services crate	1s
Build zebra-network crate	1s
Build zebra-grpc crate	1s
Build zebra-consensus crate	1s
Build zebra-chain crate	1s
Build tower-fallback crate	1s
Build tower-batch-control crate	1s
Open or update issues for building crates individually failures	0s
	22m 16s

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