adhoc fix replicas connector port with env variable

[herotai214]

Purpose

Verified with cross-node 1A1D, 1A2D, 2A2D cases with Bagel.

Saves omni_replica_id of the replica each individual process to its os.environ["VLLM_OMNI_REPLICA_ID"] under
vllm_omni/engine/stage_engine_core_proc.py

For each process, retrieve replica_id = int(os.environ.get("VLLM_OMNI_REPLICA_ID", "0")) and pass to kv_zmq_port to compute port

Test Plan

Test Result

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