[V1][PP] Support pp with ray backend in V1 (#1800)

### What this PR does / why we need it?
Support pipeline parallel with ray backend in V1Engine.

Fixes #1751

### Does this PR introduce _any_ user-facing change?
Users could specify ray as distributed backend when inferencing with pp

### How was this patch tested?
CI passed with new added test.


- vLLM version: v0.9.2
- vLLM main:
32142b3c62

---------

Signed-off-by: MengqingCao <cmq0113@163.com>

requirements-dev.txt

@@ -6,7 +6,6 @@ pytest >= 6.0
 pytest-asyncio
 pytest-mock
 lm-eval
-ray
 types-jsonschema
 xgrammar
 zmq
@@ -14,3 +13,5 @@ types-psutil
 pytest-cov
 regex
 sentence_transformers
+ray>=2.47.1
+protobuf==4.25.6