Add nix service definition for codex #4146

Job	Run time
matrix	19s
coverage	18m 18s
build / linux-unittest-amd64-pinned	16m 39s
build / linux-contract-amd64-pinned	9m 55s
build / linux-integration-amd64-pinned	39m 17s
build / linux-tools-amd64-pinned	10m 7s
build / macos-unittest-amd64-pinned	27m 16s
build / macos-contract-amd64-pinned	17m 5s
build / macos-integration-amd64-pinned	39m 18s
build / macos-tools-amd64-pinned	16m 44s
build / windows-unittest-amd64-pinned	36m 55s
build / windows-contract-amd64-pinned	19m 59s
build / windows-integration-amd64-pinned	39m 18s
build / windows-tools-amd64-pinned	22m 41s
build / status	1s
	5h 13m 52s

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