Use unit id for package key #2554

Job	Run time
cabal	29s
nix-build	57s
runghc	27s
build-extra-hackages	20s
cabal-doExactConfig	25s
hix	1m 10s
maintainer-scripts	22s
multi-target	49s
shellFor-hoogle	21s
shellFor-not-depends	31s
shellFor-multiple-package	32s
shellFor-single-package	33s
tests-benchmarks	23s
unit-tests	18s
check-path-support	14s
check-materialization-concurrency	26s
closure-size	11s
docs	47s
haskell-nix-roots-do-not-require-IFDs	13s
hix-cabal	15s
hydra-ifdLevel-0-and-1	5m 14s
hydra-ifdLevel-2	20m 13s
hydra-ifdLevel-3-and-ghc-8-10	30m 15s
hydra-ifdLevel-3-and-ghc-9-2	2h 43m 46s
hydra-without-remote-builders-ghc9101	3m 55s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	2h 48m 30s
hydra-without-remote-builders-ghc8107	8m 6s
nix-tools	4m 27s
update-docs	27s
plan-extra-hackages	40s
	6h 55m 16s

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