fix: add platform-specific functions for process management syscall

[chengfang]

Fixes #1512

Summary by CodeRabbit

• Refactor
  • Improved internal process lifecycle management for git-related operations with optimized, platform-specific behavior for Unix and Windows systems.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Pro

Run ID: 0ffae046-33fa-44e5-9157-b2e8c10b5b9a

📥 Commits

Reviewing files that changed from the base of the PR and between ad20e7e and fc7ba7d.

📒 Files selected for processing (3)

• ext/git/client.go
• ext/git/procattr_unix.go
• ext/git/procattr_windows.go

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Walkthrough

Introduces platform-specific abstractions for process group management in Git subprocess execution. Refactors client.go to use three new helper functions instead of direct syscall operations, with Unix and Windows implementations handling different timeout behaviors and process termination strategies.

Changes

Cohort / File(s)	Summary
Client refactoring ext/git/client.go	Replaces direct syscall usage (Setpgid configuration and Kill operations) with helper function calls: setSysProcAttr(), killProcessGroup(), and newTimeoutBehavior(). Removes syscall import and streamlines process management logic.
Unix-specific implementation ext/git/procattr_unix.go	Adds Unix-specific helpers that configure process groups (Setpgid), terminate process groups with SIGKILL, and set timeout behavior to use SIGTERM with ShouldWait enabled for proper subprocess cleanup on cancellation.
Windows-specific implementation ext/git/procattr_windows.go	Adds Windows-specific helpers as no-ops for process group operations (since Windows doesn't support process groups), and configures timeout behavior to use SIGKILL without waiting, adapted for Windows platform constraints.

Possibly related PRs

• #1477: Related modifications to git subprocess handling that ensure proper cleanup of child processes through structured process management helpers.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main change: introducing platform-specific helper functions to manage process syscalls across Windows and Unix platforms.
Linked Issues check	✅ Passed	The PR implementation fully addresses all coding requirements from issue #1512: adds platform-specific functions (setSysProcAttr, killProcessGroup, newTimeoutBehavior) with proper !windows and windows build tags.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the Windows build failure by refactoring syscall usage into platform-specific helpers; no unrelated modifications are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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📝 Coding Plan

• Generate coding plan for human review comments

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.62%. Comparing base (c1674be) to head (fc7ba7d).
⚠️ Report is 61 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1541      +/-   ##
==========================================
+ Coverage   71.48%   73.62%   +2.13%     
==========================================
  Files          50       53       +3     
  Lines        4667     5110     +443     
==========================================
+ Hits         3336     3762     +426     
- Misses       1133     1142       +9     
- Partials      198      206       +8     

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