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/utils/agent/agent-loop.ts

@@ -516,6 +516,7 @@ export class AgentLoop {
               stream: true,
               parallel_tool_calls: false,
               reasoning,
+              ...(this.config.flexMode ? { service_tier: "flex" } : {}),
               tools: [
                 {
                   type: "function",