pc: fix intangible_projectile NBT and 26.1 item stack templates

[u9g]

Two protocol fixes found by PrismarineJS/prismarine-item#184's live vanilla tests.

intangible_projectile is NBT, not void (1.21.5–26.1)

The component has no dedicated network codec, so vanilla syncs it through its NBT codec — an empty compound (0a 00) on the wire. 1.20.5–1.21.4 correctly had anonymousNbt and 1.21.5 onward regressed to void, leaving two bytes unread in any slot carrying the component (protodef PartialReadError on set_slot). unbreakable and glider stay void: they have real unit stream codecs and decode cleanly today.

26.1 sends non-empty stacks as item stack templates (item id first)

26.1 changed the non-optional stack codec to item id, count, components; the optional count-first Slot form (set_slot, window_items, cursor, equipment, merchant offers, entity metadata) is unchanged. Before this fix, nested stacks decode with itemId/itemCount swapped — giving bundle[bundle_contents=[{id:stone,count:3},{id:dirt}]] parsed as item 3 ×1 and item 1 ×28.

This adds an ItemStackTemplate type and uses it where vanilla uses the template codec (cross-checked against MCProtocolLib's readItemStackTemplate call sites):

• use_remainder, charged_projectiles, bundle_contents components
• container component — now a prefixed-optional template per entry, preserving empty slots
• the item particle
• the item_stack slot display
• the advancement display icon

Verification

Each site was checked against real vanilla servers (1.21.5, 1.21.6, 1.21.8, 1.21.9, 1.21.11, 26.1) by giving items carrying each component, granting an advancement and spawning item particles, then confirming the decoded ids and counts match what was given, with zero parse errors. On 26.1: stone(1)×3 + dirt(28)×1 bundle, shulker container decoding [null, diamond(899)×5], advancement icons and minecraft:item particle all correct. prismarine-item#184's 78 live window_click hash tests still pass against 1.21.5/1.21.11 with these files, now with no PartialReadErrors.

protocol.json files are regenerated from the edited proto.ymls via npm run build; tools/js tests pass (the only local failure is the 40s suite-duration gate, from running Minecraft servers concurrently on the same machine).

[rom1504]

Did you check against the decompiled code ?

[u9g]

Did you check against the decompiled code ?

I just checked, yes.

[u9g]

Decompiled sources behind each change, for the record:

• 1.21.5 DataComponents: INTANGIBLE_PROJECTILE = register("intangible_projectile", b -> b.persistent(Unit.CODEC)) with no networkSynchronized; DataComponentType.Builder.build then uses ByteBufCodecs.fromCodecWithRegistries(codec), i.e. the NBT form (empty compound). UNBREAKABLE and GLIDER are .networkSynchronized(Unit.STREAM_CODEC) and stay void. Same registrations through 26.1.
• 26.1 ItemStackTemplate.STREAM_CODEC = composite(Item.STREAM_CODEC, VAR_INT count, DataComponentPatch.STREAM_CODEC), item id first. Sites using it: UseRemainder.STREAM_CODEC, ChargedProjectiles.STREAM_CODEC (list), BundleContents.STREAM_CODEC (list), ItemContainerContents.STREAM_CODEC (.apply(ByteBufCodecs::optional).apply(list(256)), hence the prefixed optional per entry), ItemParticleOption.streamCodec, SlotDisplay.ItemStackSlotDisplay.STREAM_CODEC, DisplayInfo.serializeToNetwork (advancement icon).
• 26.1 ItemStack.STREAM_CODEC still delegates to OPTIONAL_STREAM_CODEC (count first), so MerchantOffer, set_slot, window_items, cursor, equipment and entity metadata are unchanged.