feat(c++/node): add close_outputs, NodeFailed and Reload event types

[PavelGuzenfeld]

Summary

• Add close_outputs(sender, output_ids) to selectively close node outputs from C++
• Add DoraEventType::NodeFailed and DoraEventType::Reload enum variants
• Add event_as_node_failed(event) accessor returning DoraNodeFailed struct with affected input IDs, error message, and source node ID

Stacked on #1409 (Phase 2) — merge that first, then this PR's diff is just the 1 new commit.

Usage (C++)

// Close specific outputs
rust::Vec<rust::String> ids;
ids.push_back("output_a");
auto result = close_outputs(dora_node.send_output, ids);

// Handle node failure events
if (ty == DoraEventType::NodeFailed) {
    auto failed = event_as_node_failed(std::move(event));
    std::cerr << "Node " << failed.source_node_id << " failed: " << failed.error;
}

[heyong4725]

Hi @PavelGuzenfeld — closing this in favor of #1847, which is the rescue of this PR. Second in the 4-PR rescue stack for your full series (#1409 → #1410 → #1413 → #1414); see #1846 for the first.

Same pattern as the #1846 rescue: I extracted just the named feature (NodeFailed/Reload event types + close_outputs + event_as_node_failed), kept all your work intact, adapted the event.event destructuring to the new tuple-struct DoraEvent(EventOrReason) shape that we landed in #1846 (the original PR used the named-field shape that we ended up not adopting — EventOrReason carries the no-event-available reason instead).

You're credited via Co-Authored-By on the commit. #1847 is currently stacked on #1846; once #1846 merges I'll rebase #1847 onto main.

Thanks for the work.