recalculate () {
    this._pieces.fill(0)

    for (const wire of this._torrent.wires) {
      for (let i = 0; i < this._numPieces; ++i) {
        this._pieces[i] += wire.peerPieces.get(i)
      }
    }
  }
Recalculates piece availability across all peers in the torrent.