Add era to CommonParams

[foriequal0]

No description provided.

[remagpie]

era should be monotonically increasing.
I think we need a verification logic for ChangeCommonParams checking it.

[sgkim126]

I cannot find the behavior change in 59e1696.
I think the commit title should be Extract a function to verify a new CommonParams compare to the current params

[foriequal0]

Tests are quite flaky. They are fine on my machine.