Add Qwen3 14B A8W8 kernels (#642)

## Summary

Add the Qwen3-14B A8W8 kernel implementation used by the native serving
path.

This PR keeps the existing BF16 Qwen3 path isolated and introduces
separate A8W8 prefill/decode modules for the quantized model:

- add `prefill_hidden` support for Qwen3-14B A8W8 hidden-state prefill
chunks
- add the optimized A8W8 `decode_fwd` layer kernel used by serving
decode
- handle INT8 weights, activation/weight scales, paged KV cache scale
metadata, and A8W8-specific decode constants inside the A8W8 modules
- keep scheduling, model loading, tokenizer, and request orchestration
in `pypto-serving` rather than carrying standalone lib-side runners
- keep the ordinary BF16 Qwen3-14B execution path separate from the A8W8
path

## Implementation Notes

The lib-side deliverable is intentionally limited to kernels and
kernel-adjacent compatibility:

- `models/qwen3/14b/prefill_fwd_a8w8.py` implements the A8W8 prefill
hidden path
- `models/qwen3/14b/decode_layer_a8w8.py` implements the A8W8 decode
layer path used by serving
- `golden/runner.py` compatibility changes keep generated/runtime
artifacts runnable for the JIT path
- obsolete standalone debug/golden entry points were removed during
slimming; debug-stage switches in the kernel remain available for
targeted numerical diagnosis

## Validation

End-to-end validation was run through the native serving stack with this
kernel PR plus the matching serving/backend PRs:

- prompt: `介绍一下北京故宫`
- generated tokens: 48
- output quality: normal Chinese continuation
- TTFT: `7.054s`
- TPOT: `67.8 ms/token`
- decode throughput: `14.76 tok/s`

Focused serving and PyPTO checks also passed in the matching PRs.

## Related PRs / Issues

- Tracking issue: #665
- Serving-side PR: hw-native-sys/pypto-serving#48
- PyPTO backend/lowering PR: hw-native-sys/pypto#1920

Co-authored-by: vegetabledoww <vegetabledoww@users.noreply.github.com>

Author: vegetabledoww

models/qwen3/14b/config.py

@@ -34,6 +34,8 @@
 
 # Numeric constants.
 EPS = 1e-6
+INT8_SCALE_MAX = 127.0
+INT8_AMAX_EPS = 1e-4
 HIDDEN_INV = 1.0 / HIDDEN
 HEAD_DIM_INV = 1.0 / HEAD_DIM
 ATTN_SCALE = 1.0 / (HEAD_DIM ** 0.5)