feat: power migration for nv24

[lemmih]

Summary of changes

Changes introduced in this pull request:

• Migrate power actor for nv24.
• Ramp durations are: 1 year for mainnet, 3 days for calibnet, and 200 epochs for devnet.
• No tests other than those included in the builtin actors.

Reference issue to close (if applicable)

Closes #4798

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[LesnyRumcajs]

LGTM, let's jsut change the env variable.