Support anyOf and enum in JsonSchema (#16875)

This brings us into better alignment with the JSON schema subset that is
supported in
<https://developers.openai.com/api/docs/guides/structured-outputs#supported-schemas>,
and also allows us to render richer function signatures in code mode
(e.g., anyOf{null, OtherObjectType})

codex-rs/tools/src/responses_api.rs

@@ -38,6 +38,7 @@ pub struct ResponsesApiTool {
 
 #[derive(Debug, Clone, Serialize, PartialEq)]
 #[serde(tag = "type")]
+#[allow(clippy::large_enum_variant)]
 pub enum ToolSearchOutputTool {
     #[allow(dead_code)]
     #[serde(rename = "function")]