feat: add flex mode option for cost savings (#372)

Adding in an option to turn on flex processing mode to reduce costs when
running the agent.

Bumped the openai typescript version to add the new feature.

---------

Co-authored-by: Thibault Sottiaux <tibo@openai.com>

codex-cli/src/components/singlepass-cli-app.tsx

@@ -400,6 +400,7 @@ export function SinglePassApp({
       });
       const chatResp = await openai.beta.chat.completions.parse({
         model: config.model,
+        ...(config.flexMode ? { service_tier: "flex" } : {}),
         messages: [
           {
             role: "user",