Add support for VertexAI safety settings (#624)

python/sglang/backend/vertexai.py

 import os
 import warnings
-from typing import List, Optional, Union
-
-import numpy as np
+from typing import Optional
 
 from sglang.backend.base_backend import BaseBackend
 from sglang.lang.chat_template import get_chat_template
@@ -16,12 +14,15 @@ try:
         GenerativeModel,
         Image,
     )
+    from vertexai.generative_models._generative_models import SafetySettingsType
 except ImportError as e:
     GenerativeModel = e
 
 
 class VertexAI(BaseBackend):
-    def __init__(self, model_name):
+    def __init__(
+        self, model_name, safety_settings: Optional[SafetySettingsType] = None
+    ):
         super().__init__()
 
         if isinstance(GenerativeModel, Exception):
@@ -33,6 +34,7 @@ class VertexAI(BaseBackend):
 
         self.model_name = model_name
         self.chat_template = get_chat_template("default")
+        self.safety_settings = safety_settings
 
     def get_chat_template(self):
         return self.chat_template
@@ -54,6 +56,7 @@ class VertexAI(BaseBackend):
         ret = GenerativeModel(self.model_name).generate_content(
             prompt,
             generation_config=GenerationConfig(**sampling_params.to_vertexai_kwargs()),
+            safety_settings=self.safety_settings,
         )
 
         comp = ret.text
@@ -78,6 +81,7 @@ class VertexAI(BaseBackend):
             prompt,
             stream=True,
             generation_config=GenerationConfig(**sampling_params.to_vertexai_kwargs()),
+            safety_settings=self.safety_settings,
         )
         for ret in generator:
             yield ret.text, {}