refactor: merge duplicate process termination functions into unified kill_process_tree

[garrett4wade]

Description

Merged terminate_process_tree from vllm_server.py and kill_process_tree from utils/proc.py into a single unified function in areal/utils/proc.py.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not
  work as expected)
• Documentation update
• Code refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Checklist

• I have read the Contributing Guide
• I have run formatting tools (pre-commit or manual)
• I have run relevant unit tests and they pass
• I have added tests for new functionality
• I have updated documentation if needed
• My branch is up to date with main
• This PR introduces breaking changes (if yes, fill out details below)
• If this PR changes documentation, I have built and previewed it locally with
  jb build docs
• No critical issues raised by AI reviewers (/gemini review)

[gemini-code-assist]

Summary of Changes

Hello @garrett4wade, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors the codebase by unifying disparate process termination mechanisms into a single, robust kill_process_tree utility. This change eliminates code duplication, enhances maintainability, and provides a consistent, configurable approach to gracefully or forcefully shutting down processes and their children across the application.

Highlights

• Centralized Process Termination: Consolidated multiple, duplicated process termination functions (terminate_process_tree and kill_process_tree) into a single, unified kill_process_tree utility located in areal/utils/proc.py.
• Enhanced kill_process_tree Functionality: The new utility function provides flexible options for process termination, including graceful shutdown (SIGTERM followed by SIGKILL if necessary), immediate force-killing, configurable timeouts, and the ability to include/exclude the parent process or skip specific child processes.
• Codebase-Wide Adoption: All previous instances of custom process termination logic and calls to the old duplicated functions have been replaced with calls to the new areal.utils.proc.kill_process_tree.
• Dependency Streamlining: Removed redundant imports of psutil, signal, and threading from various files, centralizing these dependencies within the new areal/utils/proc.py module.
• Updated Test Coverage: Existing unit tests related to process termination have been updated to utilize and verify the behavior of the new unified kill_process_tree function.

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[gemini-code-assist]

Code Review

This pull request is a great refactoring that successfully merges duplicated process termination logic into a single, well-documented utility function kill_process_tree. This change significantly improves code maintainability and consistency across the project. The new function is more robust, handling both graceful and aggressive termination, and its adoption simplifies the cleanup logic in multiple modules. The accompanying test updates are also well-executed, making the tests for this functionality cleaner and more direct. I've found one potential issue in the new utility function that could lead to orphaned child processes and have left a comment with a suggested fix. Overall, this is a high-quality contribution.

[nuzant]

LGTM.