fix(runtime): unify task state lifecycle with idempotent READY CAS and RUNNING promotion

[Crystal-wzy]

Summary

• Add enqueue_ready_once() to centralize PENDING → READY CAS and
  ready-queue push into a single idempotent operation. Previously the
  non-profiling path never transitioned task_state to READY, leaving
  queue state and task state inconsistent; multiple fanin observers could
  also push duplicate READY notifications. The new helper guarantees
  exactly-once enqueue via CAS, with both profiling and non-profiling
  paths sharing the same logic.
• Add push_ready_queue() / push_ready_queue_batch() helpers that wrap
  the spin-retry loop, replacing raw ready_queues[…].push() calls across
  orchestration, completion, dispatch, and local-buffer overflow paths for
  consistent retry behavior.
• Add mark_task_running_on_first_dispatch(): CAS READY → RUNNING on
  the first block dispatch (including the drain-dispatch path), completing
  the PENDING → READY → RUNNING → done state machine that was previously
  missing the RUNNING step.
• Harden completion scanning: skip cores whose running_reg_task_id is
  AICPU_TASK_INVALID; when a running FIN is observed while a pending
  dispatch exists, wait for the pending ACK/FIN before promoting, ensuring
  the payload slot is hardware-latched.
• Improve idle-iteration detection in resolve_and_dispatch: reset idle
  counter when global completed_tasks_ advances or when another scheduler
  thread still has running cores, preventing premature stall timeouts in
  multi-thread scheduling.
• Trim stall diagnostics: remove per-cluster idle/busy dump that was
  redundant with per-core logging; move CoreTracker variable after the
  ring scan for narrower scope.
• Add SPIN_WAIT_HINT() to ready-queue enqueue_pos CAS retry loop for
  reduced contention on hardware.
• Update test_task_state.cpp: NonProfilingReadyPath now asserts
  PTO2_TASK_READY instead of PTO2_TASK_PENDING, matching the unified
  state machine.

Testing

• CPU sim for models/qwen3/14b/qwen3_14b_decode.py passes after the
  READY-state fix.
• git diff --check passes for the runtime worktree.

[gemini-code-assist]

Code Review

This pull request introduces task cookie tracking in simulation and enhances the PTO2 scheduler's handling of MIX resource shapes and task state transitions. Key updates include the addition of sim_set_current_task_cookie, new queue management methods in PTO2SchedulerState, and improved synchronization logic for MIX tasks during completion and dispatch. Additionally, the non-profiling ready path now explicitly transitions tasks to the READY state. Feedback was provided regarding a potential performance regression in the push_ready_queue_batch implementation, which uses multiple single-item pushes instead of a single batch operation.