fix(cli): handle non-existing actors gracefully in F3 power proportion CLI

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

• Port feat: handle non-existing actors gracefully in F3 power proportion CLI filecoin-project/lotus#12840 to Forest

➜  lotus git:(master) ✗ lotus f3 pt gp 1179 1167 8888
{
  "Instance": 126141,
  "FromEC": false,
  "PowerTable": {
    "CID": "bafy2bzaced7pp3jghq3hdgaayl3uxcofhuedq6wwqm3pyer3oiywvqofobfto",
    "ScaledTotal": 65524
  },
  "ScaledSum": 12,
  "Proportion": 0.0001831390025028997,
  "NotFound": [
    8888
  ]
}

➜  forest git:(hm/f3-power-proportion-non-existing-actors) forest-cli f3 pt gp 1179 1167 8888
{
  "Instance": 126141,
  "FromEC": false,
  "PowerTable": {
    "CID": "bafy2bzaced7pp3jghq3hdgaayl3uxcofhuedq6wwqm3pyer3oiywvqofobfto",
    "ScaledTotal": 65524
  },
  "ScaledSum": 12,
  "Proportion": 0.0001831390025028997,
  "NotFound": [
    8888
  ]
}

Reference issue to close (if applicable)

Closes #5174

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.