战斗回放：回放记录的保留与清理

-- 错误：只加不清，过期回放点开黑屏
function saveReplay(replay)
    table.insert(replays, 1, replay)
end

local KEEP = 7 * 86400
local CAP = 20
local function cleanReplays(list)
    local now = os.time()
    local keep = {}
    for _, r in ipairs(list) do
        local expired = now - r.at > KEEP
        if r.favored or #keep < CAP then
            keep[#keep + 1] = r
        elseif expired then
            removeReplayFile(r.id)
        end
    end
    return keep
end