feat(inventory): expose NBT/component data in inventory MCP tools

Add a nullable `Nbt` field to `MccInventorySnapshotSlot`,
`MccInventorySearchMatch`, and `MccItemStackSnapshot` so that callers
can access the full item metadata beyond just material and count.

For 1.20.6+ servers the field is a map of component name
(e.g. "minecraft:custom_data") to the serialized component object.
For legacy servers it is the raw NBT dictionary. The field is omitted
entirely for vanilla items that carry no extra data, so there is no
noise for plain items like Stone or Dirt.

Implementation:
- `StructuredComponent`: add `ComponentName` property (set by the
  registry during parse) and mark both it and `TypeId` with
  `[JsonIgnore]` so they are excluded from component serialization.
- `StructuredComponentRegistry.ParseComponent`: assign `ComponentName`
  after instantiation.
- `MccGameCommon.BuildNbt`: new helper that serializes components by
  runtime type (fixing the polymorphism issue with System.Text.Json)
  keyed by component name, falling back to the legacy NBT dictionary.
- Snapshot and search query builders updated to call `BuildNbt`.

MinecraftClient/Protocol/Handlers/StructuredComponents/Core/StructuredComponent.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Text.Json.Serialization;
 using MinecraftClient.Inventory.ItemPalettes;
 
 namespace MinecraftClient.Protocol.Handlers.StructuredComponents.Core;
@@ -12,8 +13,15 @@ public abstract class StructuredComponent(DataTypes dataTypes, ItemPalette itemP
     /// <summary>
     /// The registry type ID assigned during parsing, used for round-trip serialization.
     /// </summary>
+    [JsonIgnore]
     public int TypeId { get; set; } = -1;
 
+    /// <summary>
+    /// The registry name assigned during parsing (e.g. "minecraft:custom_data"), used for NBT serialization.
+    /// </summary>
+    [JsonIgnore]
+    public string ComponentName { get; set; } = string.Empty;
+
     public abstract void Parse(Queue<byte> data);
     public abstract Queue<byte> Serialize();
 }

MinecraftClient/Protocol/Handlers/StructuredComponents/Core/StructuredComponentRegistry.cs

@@ -37,6 +37,7 @@ public abstract class StructuredComponentRegistry(DataTypes dataTypes, ItemPalet
                     ?? throw new InvalidOperationException($"Could not instantiate a parser for a structured component type {name}");
 
                 component.TypeId = id;
+                component.ComponentName = name;
                 component.Parse(data);
                 return component;
             }