Do not instantiate ServerComputer instances in the peripheral provider

Instead we create a ComputerProxy, which delegates methods to the
ServerComputer or TileComputerBase, depending on which one exists.

src/main/java/dan200/computercraft/shared/turtle/blocks/TileTurtle.java

@@ -10,6 +10,7 @@ import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.shared.computer.blocks.ComputerProxy;
 import dan200.computercraft.shared.computer.blocks.TileComputerBase;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.core.IComputer;
@@ -43,7 +44,6 @@ import net.minecraftforge.items.wrapper.InvWrapper;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 import static net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY;
 
@@ -114,6 +114,12 @@ public class TileTurtle extends TileComputerBase
         return createComputer( instanceID, id, ComputerCraft.terminalWidth_turtle, ComputerCraft.terminalHeight_turtle );
     }
 
+    @Override
+    public ComputerProxy createProxy()
+    {
+        return m_brain.getProxy();
+    }
+
     @Override
     public void destroy()
     {

src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -12,6 +12,8 @@ import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.turtle.*;
+import dan200.computercraft.shared.computer.blocks.ComputerProxy;
+import dan200.computercraft.shared.computer.blocks.TileComputerBase;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.core.IComputer;
 import dan200.computercraft.shared.computer.core.ServerComputer;
@@ -104,6 +106,7 @@ public class TurtleBrain implements ITurtleAccess
     private static final int ANIM_DURATION = 8;
 
     private TileTurtle m_owner;
+    private ComputerProxy m_proxy;
 
     private LinkedList<TurtleCommandQueueEntry> m_commandQueue;
     private int m_commandsIssued;
@@ -169,6 +172,21 @@ public class TurtleBrain implements ITurtleAccess
         return m_owner;
     }
 
+    public ComputerProxy getProxy()
+    {
+        if(m_proxy == null) {
+            m_proxy = new ComputerProxy()
+            {
+                @Override
+                protected TileComputerBase getTile()
+                {
+                    return m_owner;
+                }
+            };
+        }
+        return m_proxy;
+    }
+
     public ComputerFamily getFamily()
     {
         return m_owner.getFamily();