feat: add Flux integration and e2e tests

[Amir380-A]

What this PR does / why we need it:
Added Integration and E2E tests for Flux

Which issue(s) this PR fixes
Fixes #3256

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[Sridhar1030]

Nice work filling in the Flux test coverage gap — tests are passing and the structure looks solid. Had a few questions while reading through:

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1. Integration test assertion style — any reason not to use MakeJobSetWrapper?

The MPI integration test builds an expected JobSet with MakeJobSetWrapper and compares the whole object via BeComparableTo. The Flux test fetches the JobSet and checks individual fields with manual for i := range loops. Both work, but the manual approach won't catch unexpected extra fields/containers sneaking in.

Was there a reason the wrapper approach didn't fit here, or would it be worth aligning with the MPI pattern?

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2. What are the 3 replicated jobs?

g.Expect(jobSet.Spec.ReplicatedJobs).Should(gomega.HaveLen(3))

Only the node job is inspected after this. Could you add a quick comment noting what the other 2 are? Helps future readers understand what's expected.

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3. Suspend/resume flow — intentionally skipped?

The MPI Complete/Failed condition tests verify the Suspended=True → Suspended=False transition before checking completion. The Flux condition tests go straight from unsuspend to completion without checking the intermediate suspended state. Was that a deliberate simplification, or worth adding for parity?

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4. PR title: feat: → test:?

Since this only adds tests and a test helper with no production code changes, should the title be test: add Flux integration and e2e tests per Conventional Commits?

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Overall this looks good — just wanted to flag these before it goes further. Thanks for picking up #3256!