[None][feat] Add ZMQ KV-cache event tee with gap replay

[mohammed-deepinfra]

[None][feat] Add ZMQ KV-cache event tee with gap replay

Description

Adds an optional read-only ZMQ publisher that tees TensorRT-LLM's native KV-cache events (including token_ids, which the SSE /kv_cache_events path drops) to an external consumer such as a Dynamo RadixTree indexer, in the vLLM ZMQ wire format.

The tee is driven synchronously from the existing kv_event_processor drain loop, so it preserves the single-consumer invariant and never disturbs the production SSE path. The PUB socket is bounded (SNDHWM) with non-blocking sends a missing or slow subscriber drops events rather than backing up the engine.

Because PUB/SUB is lossy, this also adds gap replay, ported to be byte-compatible with vLLM's ZmqEventPublisher protocol so an existing Dynamo / standalone-indexer replay client works unchanged:

• A ring buffer (deque, default 10k batches) of recently published (seq, payload) pairs.
• A ROUTER socket on a dedicated daemon thread. A subscriber that detects a sequence gap sends the missing start sequence; the publisher streams back every buffered batch from that point, then an END_SEQ=-1 sentinel.

[Thachnh]

follow vllm format. kv-event-config dict instead of multiple params here