Use time limit from "meta.yaml" when test

[yzy-1]

In the current code, the program run time limit for test command of "default mode" is fixed (2 seconds). It should be loaded from meta.yaml of the problem, in the `problem.timeLimit' element.

https://github.com/cp-tools/cpt/blob/50895ecff0c62f976c455b371edd433a1f145e5e/cmd/test.go#L73