Gracefully handle fewer than 2 requests to arbitrate between

[mkorbel1]

Describe the bug

The RotateRoundRobinArbiter doesn't handle 1 request gracefully because the preference signal just gets squashed down to 0-bits.

Something like this might be better:

    final preference =
        Logic(name: 'preference', width: max(1, log2Ceil(count)));

However, we also may need to add some checks for an empty list of things to arbitrate between (illegal scenario?). We should review other arbiters (and components) for similar issues.

To Reproduce

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Expected behavior

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Actual behavior

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Additional: Dart SDK info

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Additional: pubspec.yaml

Additional: Context

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