add(mining): Restore internal miner #1985

Job	Run time
Check deny.toml bans	28s
Check Cargo.lock is up to date	1m 7s
Check deny.toml bans --features default-release-binaries	35s
Install zebrad from lockfile without cache on ubuntu-latest	8m 19s
Check deny.toml bans --all-features	27s
Test stable on ubuntu-latest	29m 22s
Check deny.toml sources	27s
Check for unused dependencies	11s
Test beta on ubuntu-latest	29m 25s
Check deny.toml sources --features default-release-binaries	30s
Test stable on macos-latest	24m 33s
Check deny.toml sources --all-features	26s
Test stable on windows-latest	47m 24s
Test beta on windows-latest	45m 10s
Open or update issues for OS integration failures	0s
	3h 8m 24s

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