强化升星：星级越高消耗指数上涨

-- 错误：线性消耗，满星毫无门槛
local cost = base * star

local BASE = 1000
local GROW = 1.5
local MAX_STAR = 12
local function upgradeCost(star)
    return math.floor(BASE * GROW ^ star)
end
local function tryUpgrade(p)
    local star = getplayvar(p, "STAR") or 0
    if star >= MAX_STAR then
        sendmsg(p, 1, "已达顶星")
        return
    end
    local cost = upgradeCost(star)
    if (getplayvar(p, "GOLD") or 0) < cost then
        sendmsg(p, 1, "金币不足，需 " .. cost)
        return
    end
    setplayvar(p, "GOLD", getplayvar(p, "GOLD") - cost)
    setplayvar(p, "STAR", star + 1)
    sendmsg(p, 1, "升星成功，当前 " .. (star + 1) .. " 星")
end