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/tests/history_notes_extension.rs

@@ -59,7 +59,7 @@ async fn installed_extension_exposes_and_invokes_history_notes_tools() -> TestRe
         .await?;
     config.model_provider.base_url = Some(format!("{}/backend-api/codex", server.uri()));
     config.token_budget = Some(TokenBudgetConfig {
-        use_history_notes_history: true,
+        use_history_notes_extension: true,
         ..TokenBudgetConfig::default()
     });
 
@@ -173,7 +173,7 @@ async fn history_notes_require_an_openai_provider_and_codex_backend_auth() -> Te
         .build()
         .await?;
     config.token_budget = Some(TokenBudgetConfig {
-        use_history_notes_history: true,
+        use_history_notes_extension: true,
         ..TokenBudgetConfig::default()
     });