fix: share cpu sim pipe state across runtime tasks

[zhoubot]

Summary

• add dynamic CPU-sim runtime hooks so the same PTO ISA call surface can resolve execution context and shared storage when running under the A5 sim runtime
• scope CPU-sim TPipe shared state by runtime task cookie as well as block/pipe metadata, so mixed tasks on the same cluster do not alias the same FIFO state
• keep the split DIR_C2V local FIFO semantics from the earlier fix, but make them safe for the cross-DSO a5sim execution model

Root Cause

The original CPU-sim split-pipe fix only covered in-process tests. In the real a5sim BGEMM flow, the producer and consumers run through separate DSOs under the host runtime, so plain header-local static pipe state is not shared across them. On top of that, reusing one shared FIFO per block was too coarse for the PTO2 scheduler, which can dispatch multiple mixed tasks on the same cluster.

This PR moves CPU-sim pipe coordination onto runtime-provided hooks and keys the shared state by task cookie, which makes the public PTO ISA interface work unchanged across CPU sim and A5.

Validation

cmake -S tests/cpu/st -B build/issue26 -DTEST_CASE=tpushpop -DCMAKE_BUILD_TYPE=Release
cmake --build build/issue26 --target tpushpop -j4
./build/issue26/bin/tpushpop

Result:

• 12/12 tests passed

End-to-end validation was also run against the real simpler a5sim BGEMM flow after the paired runtime-side fix:

source /Users/zhoubot/github/pto-orgs/simpler/.venv313/bin/activate
export PTO_ISA_ROOT=/Users/zhoubot/github/pto-isa
export CC=/opt/homebrew/bin/gcc-15
export CXX=/opt/homebrew/bin/g++-15
python /Users/zhoubot/github/pto-orgs/simpler/examples/scripts/run_example.py \
  -k /Users/zhoubot/github/pto-orgs/simpler/tests/st/a5/tensormap_and_ringbuffer/bgemm/kernels \
  -g /Users/zhoubot/github/pto-orgs/simpler/tests/st/a5/tensormap_and_ringbuffer/bgemm/golden.py \
  -p a5sim \
  --build

Result:

• TEST PASSED
• C: PASS (131072/131072 elements matched)

Related

• Sim runtime PR: fix: run a5sim bgemm through the shared pipe path simpler#397

Closes #26.