Move hal-posix-task and hal-win-task into
mruby-task/ports/posix/ and mruby-task/ports/win/.
Remove HAL auto-detection logic from mrbgem.rake. Update
cosmopolitan.rb to use conf.ports :posix instead of explicit
hal-* gem references.
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto