Allow repeating prompts if --limit exceeds the number of (filtered) prompts

[mturco]

It'd be useful if the tool allowed doing multiple eval runs on the same prompt. E.g. if --prompt-filter=foo matches 2 prompts and --limit=10 is passed, the tool could keep reusing prompts until it reaches 10. Or perhaps this behavior is gated by another --reuse-prompts flag or something.