P-chain - Cleaned up fork switch in UTs

[abi87]

Why this should be merged

In a few platformvm sub-packages, we set forks in unit test via a bunch of booleans, like

env := newEnvironment(t, false /*=postBanff*/, false /*=postCortina*/, false /*=postDurango*/)

This is annoying for a few reasons:

1. The boolean tuple gets longer with new forks
2. We can't easily signal we want the specific unit test to be valid for the latest fork, instead of specific one.

With Durango, we cleaned up unit tests in platformvm package to use an enum instead of the boolean tuples already. This PR completes the cleanup for other packages.

How this works

Just replace a tuple of boolean parameters with an enum

How this was tested

CI