feat: add MC 1.21.5 (protocol 770) support

Full protocol adaptation for Minecraft 1.21.5:

- Protocol version mapping: 770 -> 1.21.5
- Packet palette: AddExperienceOrb removed (S2C), TestInstanceBlockStatus
  added (S2C), SetTestBlock and TestInstanceBlockAction added (C2S)
- Entity metadata palette: 5 new serializer types (OptionalLivingEntityReference,
  CowVariant, WolfSoundVariant, PigVariant, ChickenVariant), OPTIONAL_UUID
  replaced by OPTIONAL_LIVING_ENTITY_REFERENCE
- Item palette: 11 new items (Bush, FireflyBush, DryShortGrass, DryTallGrass,
  Wildflowers, LeafLitter, CactusFlower, TestBlock, TestInstanceBlock,
  BlueEgg, BrownEgg)
- Entity palette: Potion split into SplashPotion and LingeringPotion
- Block palette: 9 new blocks (bush, cactus_flower, firefly_bush, leaf_litter,
  short_dry_grass, tall_dry_grass, test_block, test_instance_block, wildflowers)
- Structured components: 31 new components including tooltip_display, weapon,
  blocks_attacks, potion_duration_scale, provides_trim_material,
  provides_banner_patterns, break_sound, and 25 entity variant components;
  unbreakable changed from Bool to Unit; instrument changed to EitherHolder

Made-with: Cursor

tools/gen_entity_metadata_palette.py

@@ -37,6 +37,7 @@ FIELD_TO_ENUM = {
     "OPTIONAL_BLOCK_POS":    "OptionalPosition",
     "DIRECTION":             "Direction",
     "OPTIONAL_UUID":         "OptionalUuid",
+    "OPTIONAL_LIVING_ENTITY_REFERENCE": "OptionalLivingEntityReference",
     "BLOCK_STATE":           "BlockId",
     "OPTIONAL_BLOCK_STATE":  "OptionalBlockId",
     "COMPOUND_TAG":          "Nbt",
@@ -46,8 +47,12 @@ FIELD_TO_ENUM = {
     "OPTIONAL_UNSIGNED_INT": "OptionalVarInt",
     "POSE":                  "Pose",
     "CAT_VARIANT":           "CatVariant",
+    "COW_VARIANT":           "CowVariant",
     "WOLF_VARIANT":          "WolfVariant",
+    "WOLF_SOUND_VARIANT":    "WolfSoundVariant",
     "FROG_VARIANT":          "FrogVariant",
+    "PIG_VARIANT":           "PigVariant",
+    "CHICKEN_VARIANT":       "ChickenVariant",
     "OPTIONAL_GLOBAL_POS":   "OptionalGlobalPosition",
     "PAINTING_VARIANT":      "PaintingVariant",
     "SNIFFER_STATE":         "SnifferState",