Fix Uint32Slice param array to accept empty strings

[mkysel]

Accept empty strings in flag/env parsing by adding config.Uint32Slice and using it for config.PayerOptions.NodeSelectorPreferredNodes

Add config.Uint32Slice with UnmarshalFlag and String for comma-separated uint32 parsing, and switch PayerOptions.NodeSelectorPreferredNodes to this type in options.go. Parsing trims spaces, skips empty tokens, treats empty input as nil, and errors on non-uint32 tokens; String returns comma-separated values.

📍Where to Start

Start with config.Uint32Slice.UnmarshalFlag in custom_types.go, then review the field change in options.go.

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Macroscope summarized b39f6b0.

[api-Hypernova]

Thanks!!!