test(nns): Clean up integration test helpers (#3812) #26068

Job	Run time
Bazel Test All	35m 20s
Bazel Build Fuzzers	1m 39s
Bazel Build Fuzzers AFL	1m 34s
Bazel Build All Config Check	0s
Bazel Test macOS Intel	1h 10m 29s
Python CI Tests	1m 52s
Build IC	9m 16s
Cargo Build Release Linux	30s
Cargo Clippy Linux	26s
Build Determinism (//publish/binaries:upload, release, build-ic/release, false)	32s
Build Determinism (//publish/canisters:upload, canisters, build-ic/canisters, false)	28s
Build Determinism (//ic-os/guestos/envs/prod:upload_disk-img, guest-os/update-img, build-ic/icos/...	31s
Build Determinism (//ic-os/hostos/envs/prod:upload_update-img, host-os/update-img, build-ic/icos/...	28s
Build Determinism (//ic-os/setupos/envs/prod:upload_disk-img, setup-os/disk-img, build-ic/icos/se...	31s
	2h 3m 36s

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