Support JRuby on Windows

[jcouball]

Summary

JRuby on Windows currently does not report subprocess status: $? ($CHILD_STATUS), Process.wait, and Process.wait2 return nil. As a result, process_executer cannot detect command failures or timeouts on JRuby/Windows.

Impact

• JRuby on Windows is not supported until subprocess status is reported correctly.
• Any feature relying on exit status or timeout detection fails.

Context

• Target support: latest JRuby 9.4+ on Windows once subprocess status works.
• Current behavior: status is always nil on JRuby/Windows, blocking support.
• Repo tests: process_spawn_test/ validates JRuby subprocess behavior.
• CI: https://github.com/main-branch/process_executer/actions/workflows/process-spawn-test.yml can be run manually to verify status.

Desired outcome

• JRuby on Windows reports subprocess status so process_executer can support it.
• Tests in process_spawn_test/ confirm correct behavior on JRuby/Windows.

Steps to reproduce

1. Run the process spawn test workflow (link above) or the process_spawn_test/ suite on JRuby/Windows.
2. Observe $?, Process.wait, and Process.wait2 return nil for subprocess status.