llama_cpp server: slight refactor to init_llama function

Define an init_llama function that starts llama with supplied settings instead of just doing it in the global context of app.py

This allows the test to be less brittle by not needing to mess with os.environ, then importing the app

tests/test_llama.py

@@ -132,10 +132,11 @@ def test_utf8(monkeypatch):
 
 def test_llama_server():
     from fastapi.testclient import TestClient
-    import os
-    os.environ["MODEL"] = MODEL
-    os.environ["VOCAB_ONLY"] = "true"
-    from llama_cpp.server.app import app
+    from llama_cpp.server.app import app, init_llama, Settings
+    s = Settings()
+    s.model = MODEL
+    s.vocab_only = True
+    init_llama(s)
     client = TestClient(app)
     response = client.get("/v1/models")
     assert response.json() == {