test/scale: add api conflicts metric to scale test reporting

[rawadhossain]

Description

Extends the scale test harness to report node_readiness_api_conflicts_total metric and *ConflictExhausted failure reasons introduced in #320.

What's added

• Scale test report now includes conflict and retry exhaustion numbers.
• Added controller_runtime_reconcile_errors_total as a sanity check on retry exhaustion.
• Fixed a gap where conflicts happening between phases weren't being counted.
• Made sure that fix doesn't affect CPU, API rate, or latency numbers - those still use original measurement window.

Depends on #320

Testing

• Full scale test ran successfully.
• Verified the generated report and ran the full test/vet/lint suite.

Checklist

• make test passes
• make lint passes

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[kubernetes-prow]

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