add(mining): Restore internal miner #2579

Job	Run time
Generate crates matrix	8s
Check crates matrix	2s
Build zebrad crate	34m 40s
Build zebra-utils crate	15m 59s
Build zebra-test crate	1m 43s
Build zebra-state crate	31m 19s
Build zebra-script crate	4m 16s
Build zebra-scan crate	22m 48s
Build zebra-rpc crate	31m 21s
Build zebra-node-services crate	3m 33s
Build zebra-network crate	7m 3s
Build zebra-grpc crate	13m 30s
Build zebra-consensus crate	16m 6s
Build zebra-chain crate	5m 14s
Build tower-fallback crate	59s
Build tower-batch-control crate	1m 17s
Open or update issues for building crates individually failures	0s
	3h 9m 58s

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