Enable incremental tools by default for Responses Lite (#55368)

## What changed

Mark `incremental_tools` as stable and enable it by default. Responses Lite sessions now append tool catalog updates to request history without requiring an explicit feature opt-in.

## Testing

Run the incremental catalog scenario with the default configuration. Update assertions and snapshots for empty Responses Lite prewarm input, tool declarations on the first turn, preserved compaction history, and tool changes across model switches and child agents.

GitOrigin-RevId: 27aa6b8499d76ab12167470748452f47e14dd900

codex-rs/features/src/lib.rs

@@ -1623,8 +1623,8 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::IncrementalTools,
         key: "incremental_tools",
-        stage: Stage::UnderDevelopment,
-        default_enabled: false,
+        stage: Stage::Stable,
+        default_enabled: true,
     },
     FeatureSpec {
         id: Feature::NonPrefixedMcpToolNames,