feat(windows): refactor fs module to work with both windows and unix

[cwoolum]

Summary

This PR adds Windows support to the Amazon Q CLI by implementing platform-specific command execution and
filesystem operations. The changes ensure that the CLI works consistently across both Windows and Unix-based
systems.

Changes

• Implemented platform-specific filesystem operations in a modular structure
• Created separate modules for Unix and Windows implementations
• Added proper handling of Windows paths and symlinks
• Updated tests to use platform-agnostic paths
• Fixed permission issues that were occurring on Windows systems

Implementation Details

• Created a modular filesystem structure with platform-specific implementations:
  • fs/mod.rs: Common code and public interface
  • fs/unix.rs: Unix-specific implementations
  • fs/windows.rs: Windows-specific implementations
• Added Windows-specific symlink handling that works without admin privileges
• Implemented proper path handling for Windows using relative paths
• Updated tool registration to use platform-appropriate naming

Testing

All tests have been updated to run on both Windows and Unix platforms by:

• Using relative paths instead of absolute paths
• Handling symlinks differently based on platform
• Using platform-agnostic path manipulation

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 16.75%. Comparing base (f7cf836) to head (5727e0d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1901   +/-   ##
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  Coverage   16.75%   16.75%           
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  Files         213      213           
  Lines       20704    20704           
  Branches      871      871           
=======================================
  Hits         3468     3468           
  Misses      17236    17236           

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