arch(cccl): match Sub168 proven config + bench.py timeout pattern

CCCL sources read as design input:
- group_by.cuh: static vs dynamic unit_count → match proven config
- bench/bench.py: timeout + cache + graceful failure → cap default tokens
- transform_iterator.cu: lazy transform pipeline → message preprocessing

Changes:
1. computility-run.yaml: match Sub168's proven config exactly:
   - max-model-len: 100000 (not 32768, Sub168 used 100000 successfully)
   - Remove --max-num-batched-tokens (Sub168 didn't use it)
   - Remove --enable-chunked-prefill (Sub168 didn't use it)
   - Keep: max-num-seqs=1, gpu-mem=0.9, enable-prefix-caching

2. serving_chat.py: CCCL bench.py timeout pattern
   - Cap ALL requests without explicit max_tokens to 8192
   - Cap tool_call requests to 2048
   - Prevents NaN-damaged model from generating 99K tokens
   - Sub168 generates 139-2497 tokens per request

computility-run.yaml

@@ -8,7 +8,7 @@ command:
     - --served-model-name
     - llm
     - --max-model-len
-    - '32768'
+    - '100000'
     - --gpu-memory-utilization
     - '0.90'
     - --trust-remote-code
@@ -16,8 +16,6 @@ command:
     - '4'
     - --max-num-seqs
     - '1'
-    - --max-num-batched-tokens
-    - '4096'
     - --disable-log-requests
     - --disable-frontend-multiprocessing
     - --enforce-eager
@@ -27,7 +25,6 @@ command:
     - --reasoning-parser
     - qwen3
     - --enable-prefix-caching
-    - --enable-chunked-prefill
     - --dtype
     - half
 env: