feat(batches, completions): add /v1/completions support to /v1/batches (#3309)

# What does this PR do?

add support for /v1/completions to the /v1/batches api


## Test Plan

ci

tests/integration/recordings/responses/41e27b9b5d09.json

@@ -0,0 +1,42 @@
+{
+  "request": {
+    "method": "POST",
+    "url": "http://0.0.0.0:11434/v1/v1/completions",
+    "headers": {},
+    "body": {
+      "model": "llama3.2:3b-instruct-fp16",
+      "prompt": "Say completions",
+      "max_tokens": 20
+    },
+    "endpoint": "/v1/completions",
+    "model": "llama3.2:3b-instruct-fp16"
+  },
+  "response": {
+    "body": {
+      "__type__": "openai.types.completion.Completion",
+      "__data__": {
+        "id": "cmpl-271",
+        "choices": [
+          {
+            "finish_reason": "length",
+            "index": 0,
+            "logprobs": null,
+            "text": "You want me to respond with a completion, but you didn't specify what I should complete. Could"
+          }
+        ],
+        "created": 1756846620,
+        "model": "llama3.2:3b-instruct-fp16",
+        "object": "text_completion",
+        "system_fingerprint": "fp_ollama",
+        "usage": {
+          "completion_tokens": 20,
+          "prompt_tokens": 28,
+          "total_tokens": 48,
+          "completion_tokens_details": null,
+          "prompt_tokens_details": null
+        }
+      }
+    },
+    "is_streaming": false
+  }
+}