feat(tools)!: substantial clean up of "Tool" related datatypes (#3627)

This is a sweeping change to clean up some gunk around our "Tool"
definitions.

First, we had two types `Tool` and `ToolDef`. The first of these was a
"Resource" type for the registry but we had stopped registering tools
inside the Registry long back (and only registered ToolGroups.) The
latter was for specifying tools for the Agents API. This PR removes the
former and adds an optional `toolgroup_id` field to the latter.

Secondly, as pointed out by @bbrowning in
https://github.com/llamastack/llama-stack/pull/3003#issuecomment-3245270132,
we were doing a lossy conversion from a full JSON schema from the MCP
tool specification into our ToolDefinition to send it to the model.
There is no necessity to do this -- we ourselves aren't doing any
execution at all but merely passing it to the chat completions API which
supports this. By doing this (and by doing it poorly), we encountered
limitations like not supporting array items, or not resolving $refs,
etc.

To fix this, we replaced the `parameters` field by `{ input_schema,
output_schema }` which can be full blown JSON schemas.

Finally, there were some types in our llama-related chat format
conversion which needed some cleanup. We are taking this opportunity to
clean those up.

This PR is a substantial breaking change to the API. However, given our
window for introducing breaking changes, this suits us just fine. I will
be landing a concurrent `llama-stack-client` change as well since API
shapes are changing.

docs/static/deprecated-llama-stack-spec.yaml

@@ -3143,6 +3143,10 @@ components:
     ToolDef:
       type: object
       properties:
+        toolgroup_id:
+          type: string
+          description: >-
+            (Optional) ID of the tool group this tool belongs to
         name:
           type: string
           description: Name of the tool
@@ -3150,12 +3154,30 @@ components:
           type: string
           description: >-
             (Optional) Human-readable description of what the tool does
-        parameters:
-          type: array
-          items:
-            $ref: '#/components/schemas/ToolParameter'
+        input_schema:
+          type: object
+          additionalProperties:
+            oneOf:
+              - type: 'null'
+              - type: boolean
+              - type: number
+              - type: string
+              - type: array
+              - type: object
           description: >-
-            (Optional) List of parameters this tool accepts
+            (Optional) JSON Schema for tool inputs (MCP inputSchema)
+        output_schema:
+          type: object
+          additionalProperties:
+            oneOf:
+              - type: 'null'
+              - type: boolean
+              - type: number
+              - type: string
+              - type: array
+              - type: object
+          description: >-
+            (Optional) JSON Schema for tool outputs (MCP outputSchema)
         metadata:
           type: object
           additionalProperties:
@@ -3174,50 +3196,6 @@ components:
       title: ToolDef
       description: >-
         Tool definition used in runtime contexts.
-    ToolParameter:
-      type: object
-      properties:
-        name:
-          type: string
-          description: Name of the parameter
-        parameter_type:
-          type: string
-          description: >-
-            Type of the parameter (e.g., string, integer)
-        description:
-          type: string
-          description: >-
-            Human-readable description of what the parameter does
-        required:
-          type: boolean
-          default: true
-          description: >-
-            Whether this parameter is required for tool invocation
-        items:
-          type: object
-          description: >-
-            Type of the elements when parameter_type is array
-        title:
-          type: string
-          description: (Optional) Title of the parameter
-        default:
-          oneOf:
-            - type: 'null'
-            - type: boolean
-            - type: number
-            - type: string
-            - type: array
-            - type: object
-          description: >-
-            (Optional) Default value for the parameter if not provided
-      additionalProperties: false
-      required:
-        - name
-        - parameter_type
-        - description
-        - required
-      title: ToolParameter
-      description: Parameter definition for a tool.
     TopKSamplingStrategy:
       type: object
       properties:
@@ -3630,33 +3608,6 @@ components:
               title: BuiltinTool
             - type: string
         arguments:
-          oneOf:
-            - type: string
-            - type: object
-              additionalProperties:
-                oneOf:
-                  - type: string
-                  - type: integer
-                  - type: number
-                  - type: boolean
-                  - type: 'null'
-                  - type: array
-                    items:
-                      oneOf:
-                        - type: string
-                        - type: integer
-                        - type: number
-                        - type: boolean
-                        - type: 'null'
-                  - type: object
-                    additionalProperties:
-                      oneOf:
-                        - type: string
-                        - type: integer
-                        - type: number
-                        - type: boolean
-                        - type: 'null'
-        arguments_json:
           type: string
       additionalProperties: false
       required: