feat: update Cerebras inference provider to support dynamic model listing

- update Cerebras to use OpenAIMixin
- enable openai completions tests
- enable openai chat completions tests
- disable with n > 1 tests
- add recording for --setup cerebras --subdirs inference --pattern openai

test with: `./scripts/integration-tests.sh --stack-config server:ci-tests --setup cerebras --subdirs inference --pattern openai`

tests/integration/recordings/responses/0d3290adae1d.json

@@ -0,0 +1,93 @@
+{
+  "request": {
+    "method": "POST",
+    "url": "https://api.cerebras.ai/v1/v1/chat/completions",
+    "headers": {},
+    "body": {
+      "model": "llama-3.3-70b",
+      "messages": [
+        {
+          "role": "user",
+          "content": "What's the weather in Tokyo? Use the get_weather function to get the weather."
+        }
+      ],
+      "stream": false,
+      "tools": [
+        {
+          "type": "function",
+          "function": {
+            "name": "get_weather",
+            "description": "Get the weather in a given city",
+            "parameters": {
+              "type": "object",
+              "properties": {
+                "city": {
+                  "type": "string",
+                  "description": "The city to get the weather for"
+                }
+              }
+            }
+          }
+        }
+      ]
+    },
+    "endpoint": "/v1/chat/completions",
+    "model": "llama-3.3-70b"
+  },
+  "response": {
+    "body": {
+      "__type__": "openai.types.chat.chat_completion.ChatCompletion",
+      "__data__": {
+        "id": "chatcmpl-6228def9-c13d-4d7a-9029-e2c638a16f1b",
+        "choices": [
+          {
+            "finish_reason": "tool_calls",
+            "index": 0,
+            "logprobs": null,
+            "message": {
+              "content": null,
+              "refusal": null,
+              "role": "assistant",
+              "annotations": null,
+              "audio": null,
+              "function_call": null,
+              "tool_calls": [
+                {
+                  "id": "1c40cbc30",
+                  "function": {
+                    "arguments": "{\"city\": \"Tokyo\"}",
+                    "name": "get_weather"
+                  },
+                  "type": "function"
+                }
+              ]
+            }
+          }
+        ],
+        "created": 1758191364,
+        "model": "llama-3.3-70b",
+        "object": "chat.completion",
+        "service_tier": null,
+        "system_fingerprint": "fp_c5ec625e72d41732d8fd",
+        "usage": {
+          "completion_tokens": 12,
+          "prompt_tokens": 248,
+          "total_tokens": 260,
+          "completion_tokens_details": null,
+          "prompt_tokens_details": {
+            "audio_tokens": null,
+            "cached_tokens": 0
+          }
+        },
+        "time_info": {
+          "queue_time": 0.00041449,
+          "prompt_time": 0.007237483,
+          "completion_time": 0.003803105,
+          "total_time": 0.013348102569580078,
+          "created": 1758191364
+        }
+      }
+    },
+    "is_streaming": false
+  }
+}