[Bug][microTVM][Model Library Format]Runtime is not captured in the MLF

[mehrdadh]

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It would be great if we can capture runtime in MLF since it is very useful specially for debugging auto tuning failures in microTVM auto tuning.

cc @alanmacd @gromero

[mehrdadh]

cc @guberti @mkatanbaf @areusch

[areusch]

cc @hpanda-naut