separates platform-specific timer and interrupt code into hal-posix-task
and hal-win-task gems. mruby-task now uses HAL interface defined in
task_hal.h, making it easier to port to new platforms.
hal-posix-task: uses sigalrm/setitimer for timer, sigprocmask for irq
protection, and SA_RESTART flag to prevent EINTR on system calls.
hal-win-task: uses multimedia timer API and critical_section for irq
protection.
both HALs support multiple mrb_state instances with single shared timer.
auto-detection loads appropriate HAL based on platform.
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto