[Misc] Fix duplicate FusedMoEConfig debug messages

[njhill]

A huge number of these are logged currently (per worker, per layer)

(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
(DPEngineCoreActor pid=81393) DEBUG 07-23 07:44:18 [config.py:328] Using FusedMoEConfig::max_num_tokens=256
...

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[gemini-code-assist]

Code Review

This pull request addresses an issue with excessive duplicate debug messages from FusedMoEConfig. The change correctly replaces logger.debug with logger.debug_once, which leverages an LRU cache to ensure the message is logged only once per unique configuration within a worker. This is an effective and clean fix that improves log clarity without introducing any issues. The change is approved.