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/test_case.py

@@ -9,7 +9,10 @@ import pathlib
 
 
 class TestCase:
-    _apis = ["chat_completion", "completion"]
+    _apis = [
+        "inference/chat_completion",
+        "inference/completion",
+    ]
     _jsonblob = {}
 
     def __init__(self, name):
@@ -17,7 +20,12 @@ class TestCase:
         if self._jsonblob == {}:
             for api in self._apis:
                 with open(pathlib.Path(__file__).parent / f"{api}.json", "r") as f:
-                    TestCase._jsonblob.update({f"{api}-{k}": v for k, v in json.load(f).items()})
+                    coloned = api.replace("/", ":")
+                    try:
+                        loaded = json.load(f)
+                    except json.JSONDecodeError as e:
+                        raise ValueError(f"There is a syntax error in {api}.json: {e}") from e
+                    TestCase._jsonblob.update({f"{coloned}:{k}": v for k, v in loaded.items()})
 
         # loading this test case
         tc = self._jsonblob.get(name)
@@ -25,7 +33,6 @@ class TestCase:
             raise ValueError(f"Test case {name} not found")
 
         # these are the only fields we need
-        self.name = tc.get("name")
         self.data = tc.get("data")
 
     def __getitem__(self, key):