added caching mechanism #1454

Job	Run time
unittest	46s
collect-experiments	3s
run-test (tests/ci/rand_soc.yaml)	22m 32s
run-test (tests/ci/randsoc_dumped.yaml)	22m 31s
run-test (tests/ci/vivado_bit_analysis.yaml)	12m 58s
run-test (tests/ci/vivado_bit_to_netlist.yaml)	2m 43s
run-test (tests/ci/vivado_conformal.yaml)	42s
run-test (tests/ci/vivado_ooc.yaml)	2m 14s
run-test (tests/ci/vivado_phys_netlist.yaml)	9m 30s
run-test (tests/ci/vivado_phys_netlist_cmp.yaml)	3m 13s
run-test (tests/ci/vivado_phys_netlist_error_inject.yaml)	3m 20s
run-test (tests/ci/vivado_wafove.yaml)	2m 50s
run-test (tests/ci/vivado_yosys_impl.yaml)	4m 26s
	1h 27m 48s

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