With this PR, I can remove the original task.c in picoruby/picoruby and future development will be much easier.
## Add
### General
- C API functions exported with MRB_API for external integration:
  - mrb_execute_proc_synchronously() for synchronous proc execution
  - Task control APIs (mrb_create_task, mrb_suspend_task, mrb_resume_task, mrb_terminate_task, mrb_stop_task, mrb_task_value, mrb_task_status)
  - Task context management APIs for picoruby-sandbox (mrb_task_init_context, mrb_task_reset_context, mrb_task_proc_set)
  - Task.tick class method to get current tick count
- Comprehensive C API documentation with WASM integration examples
### For PicoRuby.wasm
- WASM/Emscripten support: Disable SIGALRM timer when __EMSCRIPTEN__ is defined, as JavaScript handles tick calls via setInterval
- Scheduler lock mechanism to prevent asynchronous task operations during synchronous execution (scheduler_lock counter in mrb_task_state)
- mrb_task_run_once() for single-step execution (event loop integration)
## Fix
### task.c
- Replace MRB_FIBER_TERMINATED with MRB_TASK_STOPPED just for clarity
- Allow suspending DORMANT and WAITING tasks in mrb_task_suspend (See comment in the source)
- Task context initialization by removing dummy callinfo push/pop
*NOTE*
With the dummy callinfo code that I deleted, IRB in PicoRuby ended SEGV.
If that code is mandatory, we need to discuss how to solve my problem.
### vm.c
- Handle MRB_TASK_CREATED status in VM's NORMAL_RETURN phase to properly stop tasks
----
These changes are necessary to make PicoRuby work.
Nevertheless, even with this patch, MicroRuby for Raspberry Pi Pico 2 is still unstable.
I would like to merge this PR anyway to make development easier by involving the PicoRuby community.