[Refactor] Modernize loop iterations and callbacks in tree-kill.ts

[gonzaloriestra]

What this PR does

This PR refactors packages/cli-kit/src/public/node/tree-kill.ts to improve code readability and maintainability:

• Replaces imperative Object.keys(tree).forEach and array .forEach loops with modern for...of loops in killAll and buildProcessTree.
• Converts function (...) callbacks to arrow functions.
• Replaces unsafe @ts-ignore comments in error handling with type checks.

How to test your changes?

CI

Checklist

• I have evaluated the impact of this change and added a risk assessment section to this PR (optional).
• I have added end-to-end tests for my changes, or determined that they are not needed.
• I have added unit tests for my changes, or determined that they are not needed.
• I have updated the documentation for affected commands/features, or determined that updates are not needed.

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PR created automatically by Jules for task 7036259734482055387 started by @gonzaloriestra

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