feat: add palettes and version constants for MC 1.21.2 (protocol 768)

Add item, entity, block, and metadata palettes for Minecraft 1.21.2:
- ItemPalette1212: 1375 items (42 new: pale oak set, colored bundles,
  creaking heart/spawn egg, banner patterns)
- EntityPalette1212: 150 entity types (boats split into per-wood-type
  entries, generic boat/chest_boat removed; added creaking,
  creaking_transient, pale oak boats)
- Palette1212 (blocks): 1084 block types with state IDs generated from
  official 1.21.2 data reports (24 new pale oak blocks, creaking heart,
  pale moss variants)
- EntityMetadataPalette: reuses 1206 (serializers unchanged in 1.21.2)

Updated version infrastructure:
- Protocol18.cs: MC_1_21_2_Version = 768, palette switch routing
- ProtocolHandler.cs: version mapping 1.21.2 <-> 768
- Program.cs: MCHighestVersion bumped to 1.21.2
- ItemType.cs, EntityType.cs, Material.cs: new enum entries

Note: packet palette, structured components, and protocol handler
changes for 1.21.2 are not yet implemented — this commit covers
palette/registry groundwork only.

Made-with: Cursor

MinecraftClient/Protocol/ProtocolHandler.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Data.Odbc;
 using System.Globalization;
@@ -153,7 +153,7 @@ namespace MinecraftClient.Protocol
             int[] suppoertedVersionsProtocol18 =
             {
                 4, 5, 47, 107, 108, 109, 110, 210, 315, 316, 335, 338, 340, 393, 401, 404, 477, 480, 485, 490, 498, 573,
-                575, 578, 735, 736, 751, 753, 754, 755, 756, 757, 758, 759, 760, 761, 762, 763, 764, 765, 766, 767
+                575, 578, 735, 736, 751, 753, 754, 755, 756, 757, 758, 759, 760, 761, 762, 763, 764, 765, 766, 767, 768
             };
 
             if (Array.IndexOf(suppoertedVersionsProtocol18, protocolVersion) > -1)
@@ -351,6 +351,8 @@ namespace MinecraftClient.Protocol
                     case "1.21":
                     case "1.21.1":
                         return 767;
+                    case "1.21.2":
+                        return 768;
                     default:
                         return 0;
                 }
@@ -432,6 +434,7 @@ namespace MinecraftClient.Protocol
                 765 => "1.20.4",
                 766 => "1.20.6",
                 767 => "1.21",
+                768 => "1.21.2",
                 _ => "0.0"
             };
         }