Add unit tests for internal/state

[abrarshivani]

Description

Raises internal/state statement coverage from 37.8% to 97.2%. Tests only — no production source changed. Tests use the controller-runtime fake client with interceptor.Funcs to inject Get/List/Create/Update errors, a fake manager, the real manifest renderer, and computed DaemonSet hashes — exercising real success and error paths rather than tautologies.

Now at 100%: info_source.go in full, and NewStateDriver, Sync, cleanupStaleDriverDaemonsets, getDaemonsetFromObjects, getObjectOfKind, getDriverName, getDriverSpec, createConfigMapVolumeMounts, buildDriverInstallConfig, renderManifestObjects, getGDSSpec/getGDRCopySpec/getRuntimeSpec, createOrUpdateObjs, isDaemonSetReady, newStates, and the stateManager methods.

The remaining ~2.8% is the reachable ceiling

Every remaining uncovered statement is genuinely not exercisable by a unit test, verified against the source:

• GetWatchSources — the uncovered block is an inline predicate.NewTypedPredicateFuncs closure only invoked by a live controller-runtime informer on a DaemonSet watch event; the outer construction is covered via a fake manager.
• NewManager / newNVIDIADriverStates success returns — require loading the hardcoded on-disk path /opt/gpu-operator/manifests/state-driver (a string literal, not an overridable var). All error paths are covered.
• getManifestObjects / handleDefaultImagesInObjects — in-loop error branches unreachable with a valid NVIDIADriver spec (the spec is always populated, so templates render and always yield a DaemonSet); the renderManifestObjects error itself is covered directly.
• mergeServiceAccount — two SetNestedField writebacks that cannot error (single top-level field on a map, value sourced from a valid NestedSlice).

Two genuine dead-code findings (not just coverage gaps)

While maximizing coverage, two blocks turned out to be unreachable due to source-level issues, worth flagging:

• driver_volumes.go (~L224-243) — the SUSE /lib/modules mount for precompiled drivers is guarded by if cr.Spec.UsePrecompiledDrivers() && ... but nested inside the enclosing if !cr.Spec.UsePrecompiledDrivers() block, a logical contradiction. This code can never execute; it looks like a real bug (precompiled-driver SUSE nodes never get /lib/modules mounted).
• nodepool.go (~L102-104) — the error branch for getOSTag, but getOSTag unconditionally returns a nil error, so it is dead.

These are left as-is in this tests-only PR; happy to address them separately if desired.

Checklist

• No secrets, sensitive information, or unrelated changes
• Lint checks passing (make lint)
• Generated assets in-sync (make validate-generated-assets)
• Go mod artifacts in-sync (make validate-modules)
• Test cases are added for new code paths

Testing

go test ./internal/state/... -covermode=count    # coverage: 97.2% of statements
golangci-lint run ./internal/state/...            # 0 issues (GOOS=linux)

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