fix: deepcopy should copy same table exactly only once #1000

Job	Run time
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/http3/admin)	9m 9s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[a-k]*)	9m 10s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[l-z]*)	9m 9s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/admin t/cli t/config-center-yaml...	9m 9s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/node t/pubsub t/router t/script ...	9m 10s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/http3/admin)	9m 9s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[a-k]*)	9m 10s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[l-z]*)	9m 10s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/admin t/cli t/config-center-yaml t/cont...	9m 9s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/node t/pubsub t/router t/script t/secre...	9m 9s
	1h 31m 34s

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