bug: timer leak in request-id plugin when reloaded

[kingluo]

Current Behavior

The timer created by this plugin is only destroyed when snowflake_inited is true.
But on some conditions, i.e. etcd_cli:keepalive(lease_id), snowflake_inited would be set to nil but keep the timer running, then plugin reload would cause a timer leak.

function _M.init()
...
    if attr.snowflake.enable then
        if process.type() == "worker" then
            ngx.timer.at(0, snowflake_init)
        end
    end
end

function _M.destroy()
    if snowflake_inited then
        timers.unregister_timer("plugin#request-id")
    end
end

local function snowflake_init()
    if snowflake_inited == nil then
...
        data_machine = gen_data_machine(max_number)
        if data_machine == nil then
            return ""
        end

...
        snowflake_inited = true
    end
end

local function gen_data_machine(max_number)
    if data_machine == nil then
...
                local handler = function()
...
                    local _, err4 = etcd_cli:keepalive(lease_id)
                    if err4 then
                        snowflake_inited = nil
                        data_machine = nil
                        core.log.error("snowflake data_machine: " .. id .." lease failed.")
                    end
                    start_at = now
                    core.log.info("snowflake data_machine: " .. id .." lease success.")
                end

                timers.register_timer("plugin#request-id", handler)
...
                break
            end
        end

        if data_machine == nil then
            core.log.error("No data_machine is not available")
            return nil
        end
    end
    return data_machine
end

Expected Behavior

No response

Error Logs

No response

Steps to Reproduce

curl http://127.0.0.1:9180/apisix/admin/plugins/reload -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT

Environment

• APISIX version (run apisix version): master branch
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):