feat: completing text /chat-completion and /completion tests (#1223)

# What does this PR do?

The goal is to have a fairly complete set of provider and e2e tests for
/chat-completion and /completion. This is the current list,
```
grep -oE "def test_[a-zA-Z_+]*" llama_stack/providers/tests/inference/test_text_inference.py | cut -d' ' -f2
```
- test_model_list
- test_text_completion_non_streaming
- test_text_completion_streaming
- test_text_completion_logprobs_non_streaming
- test_text_completion_logprobs_streaming
- test_text_completion_structured_output
- test_text_chat_completion_non_streaming
- test_text_chat_completion_structured_output
- test_text_chat_completion_streaming
- test_text_chat_completion_with_tool_calling
- test_text_chat_completion_with_tool_calling_streaming

```
grep -oE "def test_[a-zA-Z_+]*" tests/client-sdk/inference/test_text_inference.py | cut -d' ' -f2
```
- test_text_completion_non_streaming
- test_text_completion_streaming
- test_text_completion_log_probs_non_streaming
- test_text_completion_log_probs_streaming
- test_text_completion_structured_output
- test_text_chat_completion_non_streaming
- test_text_chat_completion_streaming
- test_text_chat_completion_with_tool_calling_and_non_streaming
- test_text_chat_completion_with_tool_calling_and_streaming
- test_text_chat_completion_with_tool_choice_required
- test_text_chat_completion_with_tool_choice_none
- test_text_chat_completion_structured_output
- test_text_chat_completion_tool_calling_tools_not_in_request

## Test plan

== Set up Ollama local server
```
OLLAMA_HOST=127.0.0.1:8321 with-proxy ollama serve
OLLAMA_HOST=127.0.0.1:8321 ollama run llama3.2:3b-instruct-fp16 --keepalive 60m
```

==  Run a provider test
```
conda activate stack
OLLAMA_URL="http://localhost:8321" \
pytest -v -s -k "ollama" --inference-model="llama3.2:3b-instruct-fp16" \
llama_stack/providers/tests/inference/test_text_inference.py::TestInference
```

== Run an e2e test
```
conda activate sherpa
with-proxy pip install llama-stack
export INFERENCE_MODEL=llama3.2:3b-instruct-fp16
export LLAMA_STACK_PORT=8322
with-proxy llama stack build --template ollama
with-proxy llama stack run --env OLLAMA_URL=http://localhost:8321 ollama
```
```
conda activate stack
LLAMA_STACK_PORT=8322 LLAMA_STACK_BASE_URL="http://localhost:8322" \
pytest -v -s --inference-model="llama3.2:3b-instruct-fp16" \
tests/client-sdk/inference/test_text_inference.py
```

llama_stack/providers/tests/test_cases/inference/completion.json

@@ -0,0 +1,43 @@
+{
+    "sanity": {
+        "data": {
+            "content": "Complete the sentence using one word: Roses are red, violets are "
+        }
+    },
+    "non_streaming": {
+        "data": {
+            "content": "Micheael Jordan is born in ",
+            "expected": "1963"
+        }
+    },
+    "streaming": {
+        "data": {
+            "content": "Roses are red,"
+        }
+    },
+    "log_probs": {
+        "data": {
+            "content": "Complete the sentence: Micheael Jordan is born in "
+        }
+    },
+    "logprobs_non_streaming": {
+        "data": {
+            "content": "Micheael Jordan is born in "
+        }
+    },
+    "logprobs_streaming": {
+        "data": {
+            "content": "Roses are red,"
+        }
+    },
+    "structured_output": {
+        "data": {
+            "user_input": "Michael Jordan was born in 1963. He played basketball for the Chicago Bulls. He retired in 2003.",
+            "expected": {
+                "name": "Michael Jordan",
+                "year_born": "1963",
+                "year_retired": "2003"
+            }
+        }
+    }
+}