fix(precision): guard all corex .so outputs with nan_to_num + reduce max-model-len

MoE kernels:
- topk_softmax: add .contiguous() + nan_to_num + re-normalize weights
- direct_routed: nan_to_num on w2_reduce output
- exact_reduce: nan_to_num on serial_float output

GDN kernels:
- packed_decode: nan_to_num on core_out

BI-V100 CUB may produce non-finite values in fp16 softmax/reduce.
These guards prevent garbage propagation without disabling the kernels.

max-model-len: 256000 → 131072 (4x32GB BI-V100 OOM prevention)
Dockerfile: unchanged (no force push needed)

computility-run.yaml

@@ -8,7 +8,7 @@ command:
     - --served-model-name
     - llm
     - --max-model-len
-    - '256000'
+    - '131072'
     - --gpu-memory-utilization
     - '0.95'
     - --trust-remote-code