[mcp] Improve custom MCP elicitation (#15800)

- [x] Support don't ask again for custom MCP tool calls.
- [x] Don't run arc in yolo mode.
- [x] Run arc for custom MCP tools in always allow mode.

codex-rs/core/tests/suite/code_mode.rs

@@ -207,6 +207,7 @@ async fn run_code_mode_turn_with_rmcp(
                     disabled_tools: None,
                     scopes: None,
                     oauth_resource: None,
+                    tools: HashMap::new(),
                 },
             );
             config