Enforcing NIXLv2 As default, no support for no connectors

[elevran]

Found today testing with vanilla gpu preset. The code defaults to NIXL V2. This would cause issues for someone who just wants to run vllm with P/D routing but no NIXL. System should support no connectors if desired, especially for plug and play compatibility with upstream vllm

(copied from llm-d/llm-d-routing-sidecar#25)

[shmuelk]

What does it mean to run without a connector? How is K/V transferred from the prefiller to the decoder?