Always expose nbt from turtle.getItemDetail

- Document the thread safety of DetailRegistry a little better.

 - Turtles now duplicate their inventory to the "previous
   inventory" (now called inventorySnapshot) immediately, rather than
   when the block is ticked.

   This is slightly more resource intensive, but I don't think it's so
   bad we need to worry.

 - As this snapshot is now always up-to-date, we can read it from the
   computer thread. Given the item is immutable, it's safe to read NBT
   from it.

   _Technically_ this is not safe under the Java memory model, but in
   practice I don't think we'll observe the wrong value.

Closes #1306

projects/common-api/src/main/java/dan200/computercraft/api/detail/DetailRegistry.java

@@ -32,6 +32,8 @@ public interface DetailRegistry<T> {
     /**
      * Compute basic details about an object. This is cheaper than computing all details operation, and so is suitable
      * for when you need to compute the details for a large number of values.
+     * <p>
+     * This method <em>MAY</em> be thread safe: consult the instance's documentation for details.
      *
      * @param object The object to get details for.
      * @return The basic details.
@@ -40,6 +42,8 @@ public interface DetailRegistry<T> {
 
     /**
      * Compute all details about an object, using {@link #getBasicDetails(Object)} and any registered providers.
+     * <p>
+     * This method is <em>NOT</em> thread safe. It should only be called from the computer thread.
      *
      * @param object The object to get details for.
      * @return The computed details.

projects/common-api/src/main/java/dan200/computercraft/api/detail/VanillaDetailRegistries.java

@@ -15,12 +15,17 @@ import net.minecraft.world.level.block.Block;
 public class VanillaDetailRegistries {
     /**
      * Provides details for {@link ItemStack}s.
+     * <p>
+     * This instance's {@link DetailRegistry#getBasicDetails(Object)} is thread safe (assuming the stack is immutable)
+     * and may be called from the computer thread.
      */
     public static final DetailRegistry<ItemStack> ITEM_STACK = ComputerCraftAPIService.get().getItemStackDetailRegistry();
 
     /**
      * Provides details for {@link BlockReference}, a reference to a {@link Block} in the world.
+     * <p>
+     * This instance's {@link DetailRegistry#getBasicDetails(Object)} is thread safe and may be called from the computer
+     * thread.
      */
     public static final DetailRegistry<BlockReference> BLOCK_IN_WORLD = ComputerCraftAPIService.get().getBlockInWorldDetailRegistry();
-
 }

projects/common-api/src/main/java/dan200/computercraft/api/turtle/ITurtleAccess.java

@@ -15,6 +15,7 @@ import net.minecraft.nbt.CompoundTag;
 import net.minecraft.world.Container;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.phys.Vec3;
+import org.jetbrains.annotations.ApiStatus;
 
 import javax.annotation.Nullable;
 
@@ -24,6 +25,7 @@ import javax.annotation.Nullable;
  * This should not be implemented by your classes. Do not interact with turtles except via this interface and
  * {@link ITurtleUpgrade}.
  */
+@ApiStatus.NonExtendable
 public interface ITurtleAccess {
     /**
      * Returns the world in which the turtle resides.