Rename the history notes extension config option (#39830)

## What changed

Rename the token-budget configuration key and its Rust field from
`use_history_notes_history` to `use_history_notes_extension`. Update the config
schema, extension gating, explicit-setting detection, and tests to use the new
name consistently.

GitOrigin-RevId: b6a514e23f02095fcd1d35dc42eeb7394b800c77

codex-rs/ext/history-notes/src/extension.rs

@@ -35,7 +35,7 @@ impl HistoryNotesExtension {
         if config
             .token_budget
             .as_ref()
-            .is_some_and(|token_budget| token_budget.use_history_notes_history)
+            .is_some_and(|token_budget| token_budget.use_history_notes_extension)
             && config.model_provider.is_openai()
             && self.auth_manager.current_auth_uses_codex_backend()
         {