fix: handle JSON Schema in additionalProperties for MCP tools (#4454)

Fixes #4176

Some common tools provide a schema (even if just an empty object schema)
as the value for `additionalProperties`. The parsing as it currently
stands fails when it encounters this. This PR updates the schema to
accept a schema object in addition to a boolean value, per the JSON
Schema spec.

codex-rs/core/src/tool_apply_patch.rs

@@ -116,7 +116,7 @@ It is important to remember:
         parameters: JsonSchema::Object {
             properties,
             required: Some(vec!["input".to_string()]),
-            additional_properties: Some(false),
+            additional_properties: Some(false.into()),
         },
     })
 }