recoverssm: RecoverSSM for Qwen GDN and the PLE short conv (port of upstream #58863, 03cae7837f)

Port of the upstream vLLM change #58863 (Apache-2.0). With --use-replayssm and speculative decoding, Gated DeltaNet layers verify the
draft window from a read-only checkpoint and keep a per-token replay record; after sampling one commit replays
the accepted tokens and writes the recurrent state once. The PLE short conv gets the same treatment.

Co-Authored-By: Hinata <hinata@idihore.id>
Signed-off-by: MOVZX <movzx@yahoo.com>

vllm/config/cache.py

@@ -212,7 +212,7 @@ class CacheConfig:
     mamba_block_size is a multiple of replayssm_buffer_len, but this is not
     required."""
     use_recoverssm: bool = field(default=False, init=False)
-    """Whether Kimi-K3 KDA uses RecoverSSM speculative decode."""
+    """Whether RecoverSSM speculative decode is used (Kimi-K3 KDA; Qwen4Exp GDN and PLE)."""
 
     # Will be set after profiling.
     num_gpu_blocks: int | None = field(default=None, init=False)