fx cache transceiver backend

Signed-off-by: FredricZ-2007 <226039983+fredricz-20070104@users.noreply.github.com>

Author: fredricz-20070104

tests/integration/defs/perf/disagg/test_configs/wideep/perf/deepseek-r1-fp4_1k1k_ctx2_gen1_dep48_bs16_eplb288_mtp3_ccb-DEFAULT.yaml

@@ -84,7 +84,7 @@ worker_config:
         layer_updates_per_iter: 1
     cache_transceiver_config:
       max_tokens_in_buffer: 8320
-      backend: default
+      backend: DEFAULT
     stream_interval: 20
   ctx:
     enable_layerwise_nvtx_marker: true
@@ -104,5 +104,5 @@ worker_config:
       dtype: fp8
     cache_transceiver_config:
       max_tokens_in_buffer: 8320
-      backend: default
+      backend: DEFAULT