Add child-prefab-matching repro

_REPRO/child-prefab-matching/.gitignore

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+flecs.o
+repro

_REPRO/child-prefab-matching/Troll.flecs

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+prefab Troll : Enemy {
+	HitPoints: {value: 20}
+}

_REPRO/child-prefab-matching/build-repro.sh

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+#!/usr/bin/env bash
+set -ex
+
+gcc-15 -c ../../distr/flecs.c -std=c99 -O1 -o flecs.o
+g++-15 repro.cpp flecs.o -o repro -std=c++17 -lpthread

_REPRO/child-prefab-matching/repro.cpp

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+#include <iostream>
+#include <cstdint>
+
+#include "../../distr/flecs.h"
+
+int main(int argc, char* argv[]) {
+    flecs::world world;
+
+    struct HitPoints {
+        float value;
+    };
+    world.component<HitPoints>("HitPoints")
+        .member<float>("value")
+        .set<HitPoints>({ float(10.0) });
+
+    flecs::entity enemy = world.prefab("Enemy");
+
+    if (world.script_run_file("Troll.flecs") != 0) {
+        std::cerr << "Error running script" << std::endl;
+        return 1;
+    }
+
+    flecs::entity Troll = world.lookup("Troll");
+    flecs::entity instance = world.entity().is_a(Troll);
+
+    auto q = world.query_builder()
+        .with(flecs::IsA, enemy);
+
+    // The original pattern as in https://github.com/VoxInteractive/Surwave/blob/4aa069c7fb4ccb292ffe0cd4690ec6023ccb1be6/Game/cpp/systems/enemy_death.h#L44
+    q.each([](flecs::entity e) {
+        std::cout << e.target(flecs::IsA).name() << std::endl; // prints Troll
+    });
+
+    // Recommended pattern (faster) - https://discord.com/channels/633826290415435777/1455553733978099763/1455641967605059854
+    q.each([](flecs::iter& it, size_t row) {
+        std::cout << it.pair(0).second().name() << std::endl; // prints Troll
+    });
+
+    auto repro_system = world.system<const HitPoints>("Repro")
+        .with(flecs::IsA, enemy)
+        .kind(0)
+        .run([](flecs::iter& it) {
+
+        while (it.next()) {
+            for (auto entity_index : it) {
+                flecs::entity entity = it.entity(static_cast<std::int32_t>(entity_index));
+
+                // The original pattern
+                const flecs::entity prefab_entity_via_entity_target = entity.target(flecs::IsA);
+
+                // Recommended pattern
+                const flecs::entity prefab_entity_via_it_pair = it.pair(1).second();
+
+                std::cout << prefab_entity_via_entity_target.name() << std::endl; // prints Troll
+                std::cout << prefab_entity_via_it_pair.name() << std::endl; // !!! prints Enemy
+            }
+        }
+    });
+
+    repro_system.run();
+
+    return 0;
+}