feat: support tool_choice = {required, none, <function>} (#1059)

Summary:

titled


Test Plan:

added tests and

LLAMA_STACK_CONFIG=fireworks pytest -s -v tests/client-sdk/
--safety-shield meta-llama/Llama-Guard-3-8B

docs/_static/llama-stack-spec.yaml

@@ -1637,6 +1637,7 @@ components:
           enum:
             - auto
             - required
+            - none
           description: >-
             Whether tool use is required or automatic. This is a hint to the model
             which may not be followed. It depends on the Instruction Following capabilities
@@ -1994,13 +1995,21 @@ components:
       type: object
       properties:
         tool_choice:
-          type: string
-          enum:
-            - auto
-            - required
-          description: >-
-            (Optional) Whether tool use is required or automatic. Defaults to ToolChoice.auto.
+          oneOf:
+            - type: string
+              enum:
+                - auto
+                - required
+                - none
+              description: >-
+                Whether tool use is required or automatic. This is a hint to the model
+                which may not be followed. It depends on the Instruction Following
+                capabilities of the model.
+            - type: string
           default: auto
+          description: >-
+            (Optional) Whether tool use is automatic, required, or none. Can also
+            specify a tool name to use a specific tool. Defaults to ToolChoice.auto.
         tool_prompt_format:
           type: string
           enum:
@@ -2027,8 +2036,6 @@ components:
             where the function definitions should be inserted.
           default: append
       additionalProperties: false
-      required:
-        - system_message_behavior
       description: Configuration for tool use.
     ToolDef:
       type: object
@@ -2533,6 +2540,7 @@ components:
           enum:
             - auto
             - required
+            - none
           description: >-
             Whether tool use is required or automatic. This is a hint to the model
             which may not be followed. It depends on the Instruction Following capabilities
@@ -2739,6 +2747,7 @@ components:
           enum:
             - auto
             - required
+            - none
           description: >-
             (Optional) Whether tool use is required or automatic. Defaults to ToolChoice.auto.
             .. deprecated:: Use tool_config instead.