add fakeplayer command

.fp [name] spawns a client-side RemotePlayer at your position with your
equipment (it lands in level.players(), so combat and nametag modules
see it), .fp pop fires the totem event on it, .fp swim toggles the
swim pose, .fp remove despawns it.

src/main/java/cc/fros/features/commands/impl/FakePlayerCommand.java

@@ -0,0 +1,142 @@
+package cc.fros.features.commands.impl;
+
+import com.mojang.authlib.GameProfile;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import cc.fros.features.commands.Command;
+import cc.fros.manager.CommandManager;
+import net.minecraft.client.player.RemotePlayer;
+import net.minecraft.network.protocol.game.ClientboundEntityEventPacket;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.Pose;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.UUID;
+
+public class FakePlayerCommand extends Command {
+
+    private static final byte TOTEM_POP_EVENT_ID = 35;
+
+    private static final EquipmentSlot[] COPIED_SLOTS = {
+            EquipmentSlot.MAINHAND, EquipmentSlot.OFFHAND,
+            EquipmentSlot.HEAD, EquipmentSlot.CHEST, EquipmentSlot.LEGS, EquipmentSlot.FEET
+    };
+
+    private final List<RemotePlayer> spawned = new ArrayList<>();
+    private int nextId = -13337;
+
+    public FakePlayerCommand() {
+        super("fakeplayer", "fp");
+        setDescription("Spawns a client-side fake player to test on");
+    }
+
+    @Override
+    public void createArgumentBuilder(LiteralArgumentBuilder<CommandManager> builder) {
+        builder.executes(ctx -> spawn("FakePlayer"))
+                .then(literal("remove")
+                        .executes(ctx -> removeAll()))
+                .then(literal("pop")
+                        .executes(ctx -> popAll()))
+                .then(literal("swim")
+                        .executes(ctx -> toggleSwim()))
+                .then(argument("name", StringArgumentType.word())
+                        .executes(ctx -> spawn(StringArgumentType.getString(ctx, "name"))));
+    }
+
+    private int popAll() {
+        if (nullCheck() || mc.getConnection() == null) {
+            return fail("You need to be in a world to do that.");
+        }
+
+        int popped = 0;
+        for (RemotePlayer fake : spawned) {
+            if (fake.level() != mc.level) continue;
+            mc.getConnection().handleEntityEvent(new ClientboundEntityEventPacket(fake, TOTEM_POP_EVENT_ID));
+            popped++;
+        }
+
+        if (popped == 0) {
+            return fail("No fake players to pop. Spawn one first.");
+        }
+        return success("Popped %s fake player(s)", popped);
+    }
+
+    private int toggleSwim() {
+        if (nullCheck()) {
+            return fail("You need to be in a world to do that.");
+        }
+
+        boolean anyStanding = false;
+        int found = 0;
+        for (RemotePlayer fake : spawned) {
+            if (fake.level() != mc.level) continue;
+            found++;
+            if (fake.getPose() != Pose.SWIMMING) anyStanding = true;
+        }
+        if (found == 0) {
+            return fail("No fake players. Spawn one first.");
+        }
+
+        Pose pose = anyStanding ? Pose.SWIMMING : Pose.STANDING;
+        for (RemotePlayer fake : spawned) {
+            if (fake.level() != mc.level) continue;
+            fake.setPose(pose);
+            fake.refreshDimensions();
+        }
+        return success(pose == Pose.SWIMMING
+                ? "Fake player(s) now in swim pose."
+                : "Fake player(s) now standing.");
+    }
+
+    private int spawn(String name) {
+        if (nullCheck()) {
+            return fail("You need to be in a world to do that.");
+        }
+
+        int despawned = despawnAll();
+
+        GameProfile profile = new GameProfile(UUID.randomUUID(), name);
+        RemotePlayer fake = new RemotePlayer(mc.level, profile);
+        fake.setId(nextId--);
+        fake.copyPosition(mc.player);
+        fake.setYHeadRot(mc.player.getYHeadRot());
+        fake.setHealth(20f);
+        for (EquipmentSlot slot : COPIED_SLOTS) {
+            fake.setItemSlot(slot, mc.player.getItemBySlot(slot).copy());
+        }
+        mc.level.addEntity(fake);
+        spawned.add(fake);
+        if (despawned > 0) {
+            return success("Replaced fake player with {green} %s", name);
+        }
+        return success("Spawned fake player {green} %s", name);
+    }
+
+    private int removeAll() {
+        if (nullCheck()) {
+            spawned.clear();
+            return fail("You need to be in a world to do that.");
+        }
+        int removed = despawnAll();
+        if (removed == 0) {
+            return success("No fake players to remove.");
+        }
+        return success("Removed %s fake player(s)", removed);
+    }
+
+    private int despawnAll() {
+        int removed = 0;
+        Iterator<RemotePlayer> it = spawned.iterator();
+        while (it.hasNext()) {
+            RemotePlayer fake = it.next();
+            it.remove();
+            if (fake.level() != mc.level) continue;
+            mc.level.removeEntity(fake.getId(), Entity.RemovalReason.DISCARDED);
+            removed++;
+        }
+        return removed;
+    }
+}

src/main/java/cc/fros/manager/CommandManager.java

@@ -35,6 +35,7 @@ public class CommandManager extends Feature implements Jsonable {
     public void init() {
         register(new BindCommand());
         register(new DrawnCommand());
+        register(new FakePlayerCommand());
         register(new FriendCommand());
         register(new HelpCommand());
         register(new PrefixCommand());