feat(core): add piston extend and retract block-pushing mechanics

core/include/vf/Piston.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <vector>
+#include "World.h"
+#include "Block.h"
+
+namespace vf {
+
+constexpr int pistonMaxPush = 12;
+
+struct PistonMoveResult {
+    bool moved = false;
+    int blocksPushed = 0;
+    std::vector<Vec3i> destroyed;
+};
+
+bool isPistonImmovable(Block b);
+bool isPistonFragile(Block b);
+bool isPistonBlock(Block b);
+
+PistonMoveResult extendPiston(World& world, const Vec3i& pos, Face facing);
+PistonMoveResult retractPiston(World& world, const Vec3i& pos, Face facing);
+
+} // namespace vf