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/Mapping/Material.cs

@@ -1,4 +1,4 @@
-namespace MinecraftClient.Mapping
+namespace MinecraftClient.Mapping
 {
     /// <summary>
     /// Represents Minecraft Materials
@@ -242,6 +242,7 @@
         CrackedStoneBricks,
         Crafter,
         CraftingTable,
+        CreakingHeart,
         CreeperHead,
         CreeperWallHead,
         CrimsonButton,
@@ -662,6 +663,26 @@
         OxidizedCutCopperStairs,
         PackedIce,
         PackedMud,
+        PaleHangingMoss,
+        PaleMossBlock,
+        PaleMossCarpet,
+        PaleOakButton,
+        PaleOakDoor,
+        PaleOakFence,
+        PaleOakFenceGate,
+        PaleOakHangingSign,
+        PaleOakLeaves,
+        PaleOakLog,
+        PaleOakPlanks,
+        PaleOakPressurePlate,
+        PaleOakSapling,
+        PaleOakSign,
+        PaleOakSlab,
+        PaleOakStairs,
+        PaleOakTrapdoor,
+        PaleOakWallHangingSign,
+        PaleOakWallSign,
+        PaleOakWood,
         PearlescentFroglight,
         Peony,
         PetrifiedOakSlab,
@@ -745,6 +766,7 @@
         PottedOakSapling,
         PottedOrangeTulip,
         PottedOxeyeDaisy,
+        PottedPaleOakSapling,
         PottedPinkTulip,
         PottedPoppy,
         PottedRedMushroom,
@@ -926,6 +948,8 @@
         StrippedMangroveWood,
         StrippedOakLog,
         StrippedOakWood,
+        StrippedPaleOakLog,
+        StrippedPaleOakWood,
         StrippedSpruceLog,
         StrippedSpruceWood,
         StrippedWarpedHyphae,