Fix pc/1.21.11 attribute_modifiers entry shape

[Copilot]

pc/1.21.11 encoded attribute_modifiers differently from adjacent versions: display was attached once after the list instead of per modifier entry. That breaks decoding for items carrying 2+ explicit modifiers because subsequent entries are read at the wrong offset.

• Protocol shape

  • Update data/pc/1.21.11/proto.yml so attribute_modifiers is an array of entry containers, with display nested inside each entry.
  • Regenerate data/pc/1.21.11/protocol.json from the YAML source.

• Regression coverage

  • Add a focused test asserting the generated 1.21.11 SlotComponent.attribute_modifiers shape matches the neighboring per-entry layout used by 1.21.9.

if attribute_modifiers: []varint
   typeId: varint
   name: string
   value: f64
   operation: varint => ...
   slot: varint => ...
   display:
      type: varint =>
         - default
         - hidden
         - override
      component: type ?
         if override: anonymousNbt

• Fixes pc/1.21.11: attribute_modifiers item component has display once after the list; vanilla has it per entry (breaks items with 2+ modifiers) #1252