fix(agentx): keep the measured LMCache message queue timeout on MI300X

The role connector is now the lmcache-mp preset written out plus
lmcache.mp.mq_timeout 6000, so the point keeps its measured timeout
instead of falling back to LMCache's 300 s default.

Author: camatsemianalysis

inferencex-e2e/benchmarks/single_node/srt-slurm-recipes/minimaxm3/vllm/mi300x-fp8-mtp/agentic.yaml

@@ -155,8 +155,9 @@ override_tp8_c16_lmcache:
     agg:
       args:
         max-num-seqs: 32
-        # LMCacheMPConnector to the lmcache-server service on this node (port 8750).
-        connector: lmcache-mp
+        # The lmcache-mp preset (the node's lmcache-server on port 8750) plus the
+        # measured message queue timeout.
+        connector: '{"kv_connector":"LMCacheMPConnector","kv_connector_module_path":"lmcache.integration.vllm.lmcache_mp_connector","kv_role":"kv_both","kv_connector_extra_config":{"lmcache.mp.host":"tcp://localhost","lmcache.mp.port":8750,"lmcache.mp.mq_timeout":6000.0}}'
   benchmark:
     env:
       CONC: '16'