feat(sdk): add xhigh reasoning effort support to TypeScript SDK (#8108)

Add "xhigh" to the ModelReasoningEffort type to match the Rust backend
which already supports this reasoning level for models like
gpt-5.1-codex-max.

Author: conorbranagan

sdk/typescript/src/threadOptions.ts

@@ -2,7 +2,7 @@ export type ApprovalMode = "never" | "on-request" | "on-failure" | "untrusted";
 
 export type SandboxMode = "read-only" | "workspace-write" | "danger-full-access";
 
-export type ModelReasoningEffort = "minimal" | "low" | "medium" | "high";
+export type ModelReasoningEffort = "minimal" | "low" | "medium" | "high" | "xhigh";
 
 export type ThreadOptions = {
   model?: string;