feat: support Windows processes in mcp_client

[cwoolum]

Cross-Platform Process Management for Windows Support

This PR adds cross-platform process management capabilities to support Windows in the Amazon Q Developer CLI. It addresses build issues that were occurring on Windows due to Unix-specific code.

Changes

Process Information Module

• Added from_raw method to the Pid struct for consistent process ID handling across platforms
• Implemented platform-specific terminate_process functions in their respective OS modules:
  • Uses kill with SIGTERM on Unix platforms (Linux and macOS)
  • UsesWindows API to kill processes on Windows platforms
• Updated module exports to properly expose platform-specific implementations

MCP Client

• Made process_group method conditional on Unix platforms
• Updated process termination to use the cross-platform terminate_process function
• Added fig_util as a dependency to mcp_client

Testing

• Verified that the code builds successfully on Windows

Continues work on #153

[cwoolum]

I duplicated this code for Unix and macOS since there are individual files for each OS. Not in love with it but it felt more cohesive than doing the OS specific logic in mod.rs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 16.75%. Comparing base (029f760) to head (a69178b).
Report is 25 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1765   +/-   ##
=======================================
  Coverage   16.75%   16.75%           
=======================================
  Files         213      213           
  Lines       20704    20704           
  Branches      871      871           
=======================================
  Hits         3468     3468           
  Misses      17236    17236           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[brandonskiser]

Don't add fig_util as a chat-cli dependency, instead update whatever is required to support Windows inside what we have in chat-cli