Documented meld_tiles remains empty after meld updates

[Haor]

On current main (7c9d119), the red-mahjong state documentation describes state.players.meld_tiles as the tile IDs making up each meld. However, the array is initialized to -1 and is not populated during play.

The meld update helper updates melds and meld_counts. A minimal reproduction of that update path:

import jax.numpy as jnp
from mahjax.red_mahjong.action import Action
from mahjax.red_mahjong.env import _append_meld
from mahjax.red_mahjong.meld import Meld
from mahjax.red_mahjong.state import State

pon = Meld.init(jnp.int32(Action.PON), jnp.int32(28), jnp.int32(3))
state = _append_meld(State(), pon, jnp.int32(0))
print(int(state.players.meld_counts[0]))
print(int(state.players.melds[0, 0]))
print(state.players.meld_tiles[0, 0].tolist())

Output, verified against the above commit on CPU:

1
28235
[-1, -1, -1, -1]

We encountered this in a downstream observation adapter: reading the documented array silently omitted existing meld tiles and undercounted visible tiles. Decoding state.players.melds resolved it. MahJax's own dict observation already reads the packed melds, so this report concerns the documented meld_tiles field.

Is meld_tiles intended to be populated, or is it an unused field retained in the state layout? If it is intentionally unmaintained, could the documentation and field declaration say so and point users to melds? I would like to confirm the intended contract before proposing a runtime change.