Add nix service definition for codex #4148

Job	Run time
matrix	17s
coverage	18m 52s
build / linux-unittest-amd64-pinned	16m 21s
build / linux-contract-amd64-pinned	9m 23s
build / linux-integration-amd64-pinned	1h 1m 33s
build / linux-tools-amd64-pinned	9m 51s
build / macos-unittest-amd64-pinned	30m 7s
build / macos-contract-amd64-pinned	17m 42s
build / macos-integration-amd64-pinned	1h 1m 38s
build / macos-tools-amd64-pinned	16m 33s
build / windows-unittest-amd64-pinned	34m 38s
build / windows-contract-amd64-pinned	21m 3s
build / windows-integration-amd64-pinned	1h 1m 34s
build / windows-tools-amd64-pinned	22m 29s
build / status	1s
	6h 22m 2s

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