[inference api] modify content types so they follow a more standard structure (#841)

Some small updates to the inference types to make them more standard

Specifically:
- image data is now located in a "image" subkey
- similarly tool call data is located in a "tool_call" subkey

The pattern followed is `dict(type="foo", foo=<...>)`

llama_stack/providers/tests/inference/groq/test_groq_utils.py

@@ -472,7 +472,7 @@ class TestConvertStreamChatCompletionResponse:
         iter = converted.__aiter__()
         chunk = await iter.__anext__()
         assert chunk.event.event_type == ChatCompletionResponseEventType.start
-        assert chunk.event.delta.content == ToolCall(
+        assert chunk.event.delta.tool_call == ToolCall(
             call_id="tool_call_id",
             tool_name="get_flight_info",
             arguments={"origin": "AU", "destination": "LAX"},

llama_stack/providers/tests/inference/test_text_inference.py

@@ -470,16 +470,16 @@ class TestInference:
             )
             first = grouped[ChatCompletionResponseEventType.progress][0]
             if not isinstance(
-                first.event.delta.content, ToolCall
+                first.event.delta.tool_call, ToolCall
             ):  # first chunk may contain entire call
                 assert first.event.delta.parse_status == ToolCallParseStatus.started
 
         last = grouped[ChatCompletionResponseEventType.progress][-1]
         # assert last.event.stop_reason == expected_stop_reason
         assert last.event.delta.parse_status == ToolCallParseStatus.succeeded
-        assert isinstance(last.event.delta.content, ToolCall)
+        assert isinstance(last.event.delta.tool_call, ToolCall)
 
-        call = last.event.delta.content
+        call = last.event.delta.tool_call
         assert call.tool_name == "get_weather"
         assert "location" in call.arguments
         assert "San Francisco" in call.arguments["location"]

llama_stack/providers/tests/inference/test_vision_inference.py

@@ -32,13 +32,15 @@ class TestVisionModelInference:
         "image, expected_strings",
         [
             (
-                ImageContentItem(data=PASTA_IMAGE),
+                ImageContentItem(image=dict(data=PASTA_IMAGE)),
                 ["spaghetti"],
             ),
             (
                 ImageContentItem(
-                    url=URL(
-                        uri="https://www.healthypawspetinsurance.com/Images/V3/DogAndPuppyInsurance/Dog_CTA_Desktop_HeroImage.jpg"
+                    image=dict(
+                        url=URL(
+                            uri="https://www.healthypawspetinsurance.com/Images/V3/DogAndPuppyInsurance/Dog_CTA_Desktop_HeroImage.jpg"
+                        )
                     )
                 ),
                 ["puppy"],
@@ -103,8 +105,10 @@ class TestVisionModelInference:
 
         images = [
             ImageContentItem(
-                url=URL(
-                    uri="https://www.healthypawspetinsurance.com/Images/V3/DogAndPuppyInsurance/Dog_CTA_Desktop_HeroImage.jpg"
+                image=dict(
+                    url=URL(
+                        uri="https://www.healthypawspetinsurance.com/Images/V3/DogAndPuppyInsurance/Dog_CTA_Desktop_HeroImage.jpg"
+                    )
                 )
             ),
         ]