Fix vllm port toctou

[sfc-gh-truwase]

No description provided.

[sfc-gh-mwyatt]

Suggested change

	# Pin a deterministic, per-replica base port. When many colocated
	# TP engines initialize concurrently on the same node, vLLM's
	# get_open_port() has a TOCTOU window: it binds a probe socket,
	# reads the port, closes it, and returns the number, so several
	# engines can receive the same port before any binds the TP
	# rendezvous TCPStore (tcp://127.0.0.1:<port>) -> EADDRINUSE.
	# Giving each replica a distinct VLLM_PORT base makes get_open_port
	# start from a unique value per engine; vLLM still increments from
	# the base on any residual conflict. The globally-unique replica
	# index i guarantees uniqueness across replicas colocated on the
	# same node. Disable via ARCTIC_DISABLE_VLLM_PORT_ASSIGN=1; tune the
	# range via ARCTIC_VLLM_PORT_BASE / ARCTIC_VLLM_PORT_STRIDE.
	if (self.tp_size > 1
	and os.environ.get("ARCTIC_DISABLE_VLLM_PORT_ASSIGN") != "1"):
	stride = int(os.environ.get("ARCTIC_VLLM_PORT_STRIDE", "100"))
	base = int(env.get("VLLM_PORT",
	os.environ.get("ARCTIC_VLLM_PORT_BASE", "30000")))
	env["VLLM_PORT"] = str(base + i * stride)
	# Ensure we start from offset base ports so that vllm workers do not
	# collide when attempting to obtain free ports. vLLM increments ports
	# until a free one is found, but this can lead to a race condition when
	# spinning up many replicas at the same time.
	base, stride = 30000, 100
	env["VLLM_PORT"] = str(base + i*stride)

[sfc-gh-mwyatt]

We don't need all these env vars and it's safe to apply this for any tp_size. Just simplifying and reducing AI verbosity