Ensure enough sub-processes for itk-infer

[MGAMZ]

itk-infer now will take max(args.num_proc, args.gpus) as the actual value of --num-proc, so users are allowed to only specify --gpus if they want to inference with multi-gpus.

[Copilot]

Pull request overview

Updates itk-infer CLI argument handling to ensure the spawned subprocess count is sufficient for the requested number of GPUs, enabling multi-GPU inference by specifying --gpus alone.

Changes:

• Clarified CLI help text for --num-proc and --gpus to reflect GPU round-robin assignment and the effective process count behavior.
• Added validation to reject non-positive values for --num-proc and --gpus.
• Automatically sets args.num_proc = max(args.num_proc, args.gpus) after parsing/validation.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Hits            ?     8839           
  Misses          ?     3147           
  Partials        ?      258           

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