副本进度：分步目标的计数追踪

-- 错误：每个目标各写一套变量与判定
killCount = killCount + 1
if killCount >= 30 then
    doorOpen = true
end

local function newTrack(steps)
    return {steps = steps, idx = 1}
end
local function onEvent(track, event, amount)
    local step = track.steps[track.idx]
    if step == nil or step.event ~= event then
        return
    end
    step.done = math.min((step.done or 0)
        + (amount or 1), step.target)
    refreshTrackUI(track)
    if step.done >= step.target then
        track.idx = track.idx + 1
        onStepClear(track)
    end
end
local function onStepClear(track)
    if track.idx > #track.steps then
        broadcast("副本通关")
    end
end