Support a2a3 SDMA async completion

[PKUZHOU]

Summary

• add a2a3 SDMA deferred completion support using PTO-ISA SDMA event records
• keep the existing counter completion ABI and add only the SDMA event-record completion type
• add an a2a3 SDMA async completion demo that validates producer deferred completion and consumer dependency release

Details

• pto2_defer_pto_async_event() now converts an SDMA AsyncEvent into runtime-polled event-record completion entries
• runtime polls SdmaEventRecord::flag and retires the record by clearing it and committing the completed SQ tail
• host HCCL comm can initialize a PTO-ISA SDMA workspace behind SIMPLER_ENABLE_PTO_SDMA_WORKSPACE
• fixes the non-profiling fanin-ready path to transition PENDING -> READY before queueing

Validation

• build-only: build_chip_callable("a2a3", None, "https")
• hardware: python examples/a2a3/tensormap_and_ringbuffer/sdma_async_completion_demo/test_sdma_async_completion_demo.py -p a2a3 -d 1-2 --build
  • rank 0: max_out=0.000e+00 max_result=0.000e+00
  • rank 1: max_out=0.000e+00 max_result=0.000e+00
• regression: python examples/a2a3/tensormap_and_ringbuffer/deferred_notify_demo/test_deferred_notify_demo.py -p a2a3sim -d 0-1 --build
  • rank 0/1: max_diff=0.000e+00

[gemini-code-assist]

Code Review

This pull request implements support for deferred SDMA asynchronous completion. It introduces a new demo and smoke test, integrates SDMA workspace management into the host communication layer, and extends the device-side async API to support SDMA event records. The scheduler and polling logic were updated to handle these new completion types and ensure thread-safe task transitions. Feedback was provided to include additional layout assertions for the PTO2SdmaEventRecord struct to ensure the safety of atomic operations.