【高级技巧】内容指纹：变更检测的快速比对封装

local function fingerprint(t)
    local parts = {}
    local keys = {}
    for k in pairs(t) do
        keys[#keys + 1] = tostring(k)
    end
    table.sort(keys)
    for _, k in ipairs(keys) do
        parts[#parts + 1] = k .. "=" .. tostring(t[k])
    end
    local s = table.concat(parts, ";")
    local h = 0
    for i = 1, #s do
        h = (h * 31 + string.byte(s, i)) % 4294967296
    end
    return h
end
local lastFP = nil
local function checkShopCfg(cfg)
    local fp = fingerprint(cfg)
    if lastFP == fp then
        return false
    end
    lastFP = fp
    sendmsg(nil, 1, "商店配置变更，指纹 " .. fp .. "，触发重建。")
    return true
end

local changed = checkShopCfg(shopCfg)