Fix ActionIfIsolated::DoNothing infinite loop when all species are isolated

[Copilot]

When ActionIfIsolated::DoNothing is selected and every species has fewer than 2 members, the repopulation loop spins forever — i is never incremented because every iteration hits continue without producing an offspring.

Changes

• Pre-loop guard in SpeciatedCrossoverRepopulator::repopulate: Before entering the main loop, checks whether any species has ≥ 2 members when DoNothing is active. If none do, delegates immediately to inner.repopulate and returns — ensuring the loop is never entered in the degenerate case.
• Updated DoNothing doc comment: Documents the fallback behaviour instead of the previous note that a hang was "possible".

// New guard before the main loop
if matches!(self.action_if_isolated, ActionIfIsolated::DoNothing)
    && !population.species.iter().any(|s| s.len() >= 2)
{
    self.inner.repopulate(genomes, target_size);
    return;
}

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.