Record reasoning effort changes in conversation history behind a flag (#43110)

## What changed

Add the disabled-by-default `reasoning_effort_override` feature for OpenAI models with `use_responses_lite` enabled. Append a trusted `configuration_update` after accepted input when no effort is established in surviving history or the resolved effort changes. Preserve the existing history prefix and continue sending the request-level reasoning effort.

Share effort normalization through `ModelInfo::resolve_reasoning_effort` so requests and history updates resolve `ultra` consistently and translate `persistent` to `disabled`. Exclude other custom effort values from history updates, and compare only against harness-authored configuration items.

## Testing

Add integration coverage for effort transitions, deduplication, history prefix and cache-key preservation, alias normalization, and feature/provider/model gating. Add unit coverage for model-specific `ultra` resolution, fallbacks, and `persistent` translation.

GitOrigin-RevId: c3fe7050058076454d8ea20054a618bca9d48c7c

codex-rs/core/config.schema.json

@@ -879,6 +879,9 @@
             "realtime_conversation": {
               "type": "boolean"
             },
+            "reasoning_effort_override": {
+              "type": "boolean"
+            },
             "recommended_plugins": {
               "type": "boolean"
             },
@@ -6271,6 +6274,9 @@
         "realtime_conversation": {
           "type": "boolean"
         },
+        "reasoning_effort_override": {
+          "type": "boolean"
+        },
         "recommended_plugins": {
           "type": "boolean"
         },